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eacd6f04 PM |
1 | /* SPDX-License-Identifier: GPL-2.0+ */ |
2 | /* | |
3 | * Task-based RCU implementations. | |
4 | * | |
5 | * Copyright (C) 2020 Paul E. McKenney | |
6 | */ | |
7 | ||
8fd8ca38 | 8 | #ifdef CONFIG_TASKS_RCU_GENERIC |
9b073de1 | 9 | #include "rcu_segcblist.h" |
5873b8a9 PM |
10 | |
11 | //////////////////////////////////////////////////////////////////////// | |
12 | // | |
13 | // Generic data structures. | |
14 | ||
15 | struct rcu_tasks; | |
16 | typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp); | |
7460ade1 | 17 | typedef void (*pregp_func_t)(struct list_head *hop); |
e4fe5dd6 | 18 | typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop); |
9796e1ae | 19 | typedef void (*postscan_func_t)(struct list_head *hop); |
e4fe5dd6 | 20 | typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp); |
af051ca4 | 21 | typedef void (*postgp_func_t)(struct rcu_tasks *rtp); |
eacd6f04 | 22 | |
07e10515 | 23 | /** |
cafafd67 | 24 | * struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism. |
9b073de1 | 25 | * @cblist: Callback list. |
381a4f3b | 26 | * @lock: Lock protecting per-CPU callback list. |
7d13d30b | 27 | * @rtp_jiffies: Jiffies counter value for statistics. |
d119357d PM |
28 | * @lazy_timer: Timer to unlazify callbacks. |
29 | * @urgent_gp: Number of additional non-lazy grace periods. | |
7d13d30b | 30 | * @rtp_n_lock_retries: Rough lock-contention statistic. |
d363f833 | 31 | * @rtp_work: Work queue for invoking callbacks. |
3063b33a | 32 | * @rtp_irq_work: IRQ work queue for deferred wakeups. |
ce9b1c66 | 33 | * @barrier_q_head: RCU callback for barrier operation. |
434c9eef | 34 | * @rtp_blkd_tasks: List of tasks blocked as readers. |
bfe93930 | 35 | * @rtp_exit_list: List of tasks in the latter portion of do_exit(). |
ce9b1c66 PM |
36 | * @cpu: CPU number corresponding to this entry. |
37 | * @rtpp: Pointer to the rcu_tasks structure. | |
cafafd67 PM |
38 | */ |
39 | struct rcu_tasks_percpu { | |
9b073de1 | 40 | struct rcu_segcblist cblist; |
381a4f3b | 41 | raw_spinlock_t __private lock; |
7d13d30b PM |
42 | unsigned long rtp_jiffies; |
43 | unsigned long rtp_n_lock_retries; | |
d119357d PM |
44 | struct timer_list lazy_timer; |
45 | unsigned int urgent_gp; | |
d363f833 | 46 | struct work_struct rtp_work; |
3063b33a | 47 | struct irq_work rtp_irq_work; |
ce9b1c66 | 48 | struct rcu_head barrier_q_head; |
434c9eef | 49 | struct list_head rtp_blkd_tasks; |
bfe93930 | 50 | struct list_head rtp_exit_list; |
d363f833 PM |
51 | int cpu; |
52 | struct rcu_tasks *rtpp; | |
cafafd67 PM |
53 | }; |
54 | ||
55 | /** | |
56 | * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism. | |
88db792b | 57 | * @cbs_wait: RCU wait allowing a new callback to get kthread's attention. |
cafafd67 | 58 | * @cbs_gbl_lock: Lock protecting callback list. |
d96225fd | 59 | * @tasks_gp_mutex: Mutex protecting grace period, needed during mid-boot dead zone. |
5873b8a9 | 60 | * @gp_func: This flavor's grace-period-wait function. |
af051ca4 | 61 | * @gp_state: Grace period's most recent state transition (debugging). |
4fe192df | 62 | * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping. |
2393a613 | 63 | * @init_fract: Initial backoff sleep interval. |
af051ca4 PM |
64 | * @gp_jiffies: Time of last @gp_state transition. |
65 | * @gp_start: Most recent grace-period start in jiffies. | |
b14fb4fb | 66 | * @tasks_gp_seq: Number of grace periods completed since boot. |
238dbce3 | 67 | * @n_ipis: Number of IPIs sent to encourage grace periods to end. |
7e0669c3 | 68 | * @n_ipis_fails: Number of IPI-send failures. |
d119357d PM |
69 | * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. |
70 | * @lazy_jiffies: Number of jiffies to allow callbacks to be lazy. | |
e4fe5dd6 PM |
71 | * @pregp_func: This flavor's pre-grace-period function (optional). |
72 | * @pertask_func: This flavor's per-task scan function (optional). | |
73 | * @postscan_func: This flavor's post-task scan function (optional). | |
85b86994 | 74 | * @holdouts_func: This flavor's holdout-list scan function (optional). |
e4fe5dd6 | 75 | * @postgp_func: This flavor's post-grace-period function (optional). |
5873b8a9 | 76 | * @call_func: This flavor's call_rcu()-equivalent function. |
cafafd67 | 77 | * @rtpcpu: This flavor's rcu_tasks_percpu structure. |
7a30871b | 78 | * @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks. |
2cee0789 PM |
79 | * @percpu_enqueue_lim: Number of per-CPU callback queues in use for enqueuing. |
80 | * @percpu_dequeue_lim: Number of per-CPU callback queues in use for dequeuing. | |
fd796e41 | 81 | * @percpu_dequeue_gpseq: RCU grace-period number to propagate enqueue limit to dequeuers. |
ce9b1c66 PM |
82 | * @barrier_q_mutex: Serialize barrier operations. |
83 | * @barrier_q_count: Number of queues being waited on. | |
84 | * @barrier_q_completion: Barrier wait/wakeup mechanism. | |
85 | * @barrier_q_seq: Sequence number for barrier operations. | |
c97d12a6 PM |
86 | * @name: This flavor's textual name. |
87 | * @kname: This flavor's kthread name. | |
07e10515 PM |
88 | */ |
89 | struct rcu_tasks { | |
88db792b | 90 | struct rcuwait cbs_wait; |
cafafd67 | 91 | raw_spinlock_t cbs_gbl_lock; |
d96225fd | 92 | struct mutex tasks_gp_mutex; |
af051ca4 | 93 | int gp_state; |
4fe192df | 94 | int gp_sleep; |
2393a613 | 95 | int init_fract; |
af051ca4 | 96 | unsigned long gp_jiffies; |
88092d0c | 97 | unsigned long gp_start; |
b14fb4fb | 98 | unsigned long tasks_gp_seq; |
238dbce3 | 99 | unsigned long n_ipis; |
7e0669c3 | 100 | unsigned long n_ipis_fails; |
07e10515 | 101 | struct task_struct *kthread_ptr; |
d119357d | 102 | unsigned long lazy_jiffies; |
5873b8a9 | 103 | rcu_tasks_gp_func_t gp_func; |
e4fe5dd6 PM |
104 | pregp_func_t pregp_func; |
105 | pertask_func_t pertask_func; | |
106 | postscan_func_t postscan_func; | |
107 | holdouts_func_t holdouts_func; | |
108 | postgp_func_t postgp_func; | |
5873b8a9 | 109 | call_rcu_func_t call_func; |
cafafd67 | 110 | struct rcu_tasks_percpu __percpu *rtpcpu; |
7a30871b | 111 | int percpu_enqueue_shift; |
8dd593fd | 112 | int percpu_enqueue_lim; |
2cee0789 | 113 | int percpu_dequeue_lim; |
fd796e41 | 114 | unsigned long percpu_dequeue_gpseq; |
ce9b1c66 PM |
115 | struct mutex barrier_q_mutex; |
116 | atomic_t barrier_q_count; | |
117 | struct completion barrier_q_completion; | |
118 | unsigned long barrier_q_seq; | |
c97d12a6 PM |
119 | char *name; |
120 | char *kname; | |
07e10515 PM |
121 | }; |
122 | ||
3063b33a PM |
123 | static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp); |
124 | ||
cafafd67 PM |
125 | #define DEFINE_RCU_TASKS(rt_name, gp, call, n) \ |
126 | static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \ | |
381a4f3b | 127 | .lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \ |
88db792b | 128 | .rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup), \ |
cafafd67 PM |
129 | }; \ |
130 | static struct rcu_tasks rt_name = \ | |
131 | { \ | |
88db792b | 132 | .cbs_wait = __RCUWAIT_INITIALIZER(rt_name.wait), \ |
cafafd67 | 133 | .cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock), \ |
d96225fd | 134 | .tasks_gp_mutex = __MUTEX_INITIALIZER(rt_name.tasks_gp_mutex), \ |
cafafd67 PM |
135 | .gp_func = gp, \ |
136 | .call_func = call, \ | |
137 | .rtpcpu = &rt_name ## __percpu, \ | |
d119357d | 138 | .lazy_jiffies = DIV_ROUND_UP(HZ, 4), \ |
cafafd67 | 139 | .name = n, \ |
2bcd18e0 | 140 | .percpu_enqueue_shift = order_base_2(CONFIG_NR_CPUS), \ |
8dd593fd | 141 | .percpu_enqueue_lim = 1, \ |
2cee0789 | 142 | .percpu_dequeue_lim = 1, \ |
ce9b1c66 PM |
143 | .barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \ |
144 | .barrier_q_seq = (0UL - 50UL) << RCU_SEQ_CTR_SHIFT, \ | |
cafafd67 | 145 | .kname = #rt_name, \ |
07e10515 PM |
146 | } |
147 | ||
2b4be548 | 148 | #ifdef CONFIG_TASKS_RCU |
eacd6f04 | 149 | |
a4533cc0 NU |
150 | /* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */ |
151 | static void tasks_rcu_exit_srcu_stall(struct timer_list *unused); | |
152 | static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall); | |
153 | #endif | |
154 | ||
b0afa0f0 | 155 | /* Avoid IPIing CPUs early in the grace period. */ |
574de876 | 156 | #define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0) |
b0afa0f0 PM |
157 | static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY; |
158 | module_param(rcu_task_ipi_delay, int, 0644); | |
159 | ||
eacd6f04 | 160 | /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ |
1cf1144e | 161 | #define RCU_TASK_BOOT_STALL_TIMEOUT (HZ * 30) |
eacd6f04 PM |
162 | #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10) |
163 | static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT; | |
164 | module_param(rcu_task_stall_timeout, int, 0644); | |
f2539003 PM |
165 | #define RCU_TASK_STALL_INFO (HZ * 10) |
166 | static int rcu_task_stall_info __read_mostly = RCU_TASK_STALL_INFO; | |
167 | module_param(rcu_task_stall_info, int, 0644); | |
168 | static int rcu_task_stall_info_mult __read_mostly = 3; | |
169 | module_param(rcu_task_stall_info_mult, int, 0444); | |
eacd6f04 | 170 | |
8610b656 PM |
171 | static int rcu_task_enqueue_lim __read_mostly = -1; |
172 | module_param(rcu_task_enqueue_lim, int, 0444); | |
173 | ||
ab97152f PM |
174 | static bool rcu_task_cb_adjust; |
175 | static int rcu_task_contend_lim __read_mostly = 100; | |
176 | module_param(rcu_task_contend_lim, int, 0444); | |
fd796e41 PM |
177 | static int rcu_task_collapse_lim __read_mostly = 10; |
178 | module_param(rcu_task_collapse_lim, int, 0444); | |
db13710a PM |
179 | static int rcu_task_lazy_lim __read_mostly = 32; |
180 | module_param(rcu_task_lazy_lim, int, 0444); | |
ab97152f | 181 | |
af051ca4 PM |
182 | /* RCU tasks grace-period state for debugging. */ |
183 | #define RTGS_INIT 0 | |
184 | #define RTGS_WAIT_WAIT_CBS 1 | |
185 | #define RTGS_WAIT_GP 2 | |
186 | #define RTGS_PRE_WAIT_GP 3 | |
187 | #define RTGS_SCAN_TASKLIST 4 | |
188 | #define RTGS_POST_SCAN_TASKLIST 5 | |
189 | #define RTGS_WAIT_SCAN_HOLDOUTS 6 | |
190 | #define RTGS_SCAN_HOLDOUTS 7 | |
191 | #define RTGS_POST_GP 8 | |
192 | #define RTGS_WAIT_READERS 9 | |
193 | #define RTGS_INVOKE_CBS 10 | |
194 | #define RTGS_WAIT_CBS 11 | |
8344496e | 195 | #ifndef CONFIG_TINY_RCU |
af051ca4 PM |
196 | static const char * const rcu_tasks_gp_state_names[] = { |
197 | "RTGS_INIT", | |
198 | "RTGS_WAIT_WAIT_CBS", | |
199 | "RTGS_WAIT_GP", | |
200 | "RTGS_PRE_WAIT_GP", | |
201 | "RTGS_SCAN_TASKLIST", | |
202 | "RTGS_POST_SCAN_TASKLIST", | |
203 | "RTGS_WAIT_SCAN_HOLDOUTS", | |
204 | "RTGS_SCAN_HOLDOUTS", | |
205 | "RTGS_POST_GP", | |
206 | "RTGS_WAIT_READERS", | |
207 | "RTGS_INVOKE_CBS", | |
208 | "RTGS_WAIT_CBS", | |
209 | }; | |
8344496e | 210 | #endif /* #ifndef CONFIG_TINY_RCU */ |
af051ca4 | 211 | |
5873b8a9 PM |
212 | //////////////////////////////////////////////////////////////////////// |
213 | // | |
214 | // Generic code. | |
215 | ||
d363f833 PM |
216 | static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp); |
217 | ||
af051ca4 PM |
218 | /* Record grace-period phase and time. */ |
219 | static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate) | |
220 | { | |
221 | rtp->gp_state = newstate; | |
222 | rtp->gp_jiffies = jiffies; | |
223 | } | |
224 | ||
8344496e | 225 | #ifndef CONFIG_TINY_RCU |
af051ca4 PM |
226 | /* Return state name. */ |
227 | static const char *tasks_gp_state_getname(struct rcu_tasks *rtp) | |
228 | { | |
229 | int i = data_race(rtp->gp_state); // Let KCSAN detect update races | |
230 | int j = READ_ONCE(i); // Prevent the compiler from reading twice | |
231 | ||
232 | if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names)) | |
233 | return "???"; | |
234 | return rcu_tasks_gp_state_names[j]; | |
235 | } | |
8344496e | 236 | #endif /* #ifndef CONFIG_TINY_RCU */ |
af051ca4 | 237 | |
cafafd67 | 238 | // Initialize per-CPU callback lists for the specified flavor of |
cb88f7f5 | 239 | // Tasks RCU. Do not enqueue callbacks before this function is invoked. |
cafafd67 PM |
240 | static void cblist_init_generic(struct rcu_tasks *rtp) |
241 | { | |
242 | int cpu; | |
8610b656 | 243 | int lim; |
da123016 | 244 | int shift; |
cafafd67 | 245 | |
ab97152f PM |
246 | if (rcu_task_enqueue_lim < 0) { |
247 | rcu_task_enqueue_lim = 1; | |
248 | rcu_task_cb_adjust = true; | |
ab97152f | 249 | } else if (rcu_task_enqueue_lim == 0) { |
8610b656 | 250 | rcu_task_enqueue_lim = 1; |
ab97152f | 251 | } |
8610b656 PM |
252 | lim = rcu_task_enqueue_lim; |
253 | ||
254 | if (lim > nr_cpu_ids) | |
255 | lim = nr_cpu_ids; | |
da123016 PM |
256 | shift = ilog2(nr_cpu_ids / lim); |
257 | if (((nr_cpu_ids - 1) >> shift) >= lim) | |
258 | shift++; | |
259 | WRITE_ONCE(rtp->percpu_enqueue_shift, shift); | |
2cee0789 | 260 | WRITE_ONCE(rtp->percpu_dequeue_lim, lim); |
8610b656 | 261 | smp_store_release(&rtp->percpu_enqueue_lim, lim); |
cafafd67 PM |
262 | for_each_possible_cpu(cpu) { |
263 | struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); | |
264 | ||
265 | WARN_ON_ONCE(!rtpcp); | |
266 | if (cpu) | |
381a4f3b | 267 | raw_spin_lock_init(&ACCESS_PRIVATE(rtpcp, lock)); |
9b073de1 PM |
268 | if (rcu_segcblist_empty(&rtpcp->cblist)) |
269 | rcu_segcblist_init(&rtpcp->cblist); | |
d363f833 PM |
270 | INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq); |
271 | rtpcp->cpu = cpu; | |
272 | rtpcp->rtpp = rtp; | |
434c9eef PM |
273 | if (!rtpcp->rtp_blkd_tasks.next) |
274 | INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); | |
46faf9d8 PM |
275 | if (!rtpcp->rtp_exit_list.next) |
276 | INIT_LIST_HEAD(&rtpcp->rtp_exit_list); | |
cafafd67 | 277 | } |
5fc8cbe4 | 278 | |
edff5e9a Z |
279 | pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name, |
280 | data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim), rcu_task_cb_adjust); | |
cafafd67 PM |
281 | } |
282 | ||
d119357d PM |
283 | // Compute wakeup time for lazy callback timer. |
284 | static unsigned long rcu_tasks_lazy_time(struct rcu_tasks *rtp) | |
285 | { | |
286 | return jiffies + rtp->lazy_jiffies; | |
287 | } | |
288 | ||
289 | // Timer handler that unlazifies lazy callbacks. | |
290 | static void call_rcu_tasks_generic_timer(struct timer_list *tlp) | |
291 | { | |
292 | unsigned long flags; | |
293 | bool needwake = false; | |
294 | struct rcu_tasks *rtp; | |
295 | struct rcu_tasks_percpu *rtpcp = from_timer(rtpcp, tlp, lazy_timer); | |
296 | ||
297 | rtp = rtpcp->rtpp; | |
298 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
299 | if (!rcu_segcblist_empty(&rtpcp->cblist) && rtp->lazy_jiffies) { | |
300 | if (!rtpcp->urgent_gp) | |
301 | rtpcp->urgent_gp = 1; | |
302 | needwake = true; | |
303 | mod_timer(&rtpcp->lazy_timer, rcu_tasks_lazy_time(rtp)); | |
304 | } | |
305 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
306 | if (needwake) | |
307 | rcuwait_wake_up(&rtp->cbs_wait); | |
308 | } | |
309 | ||
3063b33a PM |
310 | // IRQ-work handler that does deferred wakeup for call_rcu_tasks_generic(). |
311 | static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp) | |
312 | { | |
313 | struct rcu_tasks *rtp; | |
314 | struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work); | |
315 | ||
316 | rtp = rtpcp->rtpp; | |
88db792b | 317 | rcuwait_wake_up(&rtp->cbs_wait); |
3063b33a PM |
318 | } |
319 | ||
5873b8a9 PM |
320 | // Enqueue a callback for the specified flavor of Tasks RCU. |
321 | static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, | |
322 | struct rcu_tasks *rtp) | |
eacd6f04 | 323 | { |
07d95c34 | 324 | int chosen_cpu; |
eacd6f04 | 325 | unsigned long flags; |
d119357d | 326 | bool havekthread = smp_load_acquire(&rtp->kthread_ptr); |
07d95c34 | 327 | int ideal_cpu; |
7d13d30b | 328 | unsigned long j; |
ab97152f | 329 | bool needadjust = false; |
eacd6f04 | 330 | bool needwake; |
cafafd67 | 331 | struct rcu_tasks_percpu *rtpcp; |
eacd6f04 PM |
332 | |
333 | rhp->next = NULL; | |
334 | rhp->func = func; | |
cafafd67 | 335 | local_irq_save(flags); |
fd796e41 | 336 | rcu_read_lock(); |
07d95c34 ED |
337 | ideal_cpu = smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift); |
338 | chosen_cpu = cpumask_next(ideal_cpu - 1, cpu_possible_mask); | |
339 | rtpcp = per_cpu_ptr(rtp->rtpcpu, chosen_cpu); | |
7d13d30b PM |
340 | if (!raw_spin_trylock_rcu_node(rtpcp)) { // irqs already disabled. |
341 | raw_spin_lock_rcu_node(rtpcp); // irqs already disabled. | |
342 | j = jiffies; | |
343 | if (rtpcp->rtp_jiffies != j) { | |
344 | rtpcp->rtp_jiffies = j; | |
345 | rtpcp->rtp_n_lock_retries = 0; | |
346 | } | |
ab97152f PM |
347 | if (rcu_task_cb_adjust && ++rtpcp->rtp_n_lock_retries > rcu_task_contend_lim && |
348 | READ_ONCE(rtp->percpu_enqueue_lim) != nr_cpu_ids) | |
349 | needadjust = true; // Defer adjustment to avoid deadlock. | |
7d13d30b | 350 | } |
cb88f7f5 PM |
351 | // Queuing callbacks before initialization not yet supported. |
352 | if (WARN_ON_ONCE(!rcu_segcblist_is_enabled(&rtpcp->cblist))) | |
353 | rcu_segcblist_init(&rtpcp->cblist); | |
db13710a PM |
354 | needwake = (func == wakeme_after_rcu) || |
355 | (rcu_segcblist_n_cbs(&rtpcp->cblist) == rcu_task_lazy_lim); | |
356 | if (havekthread && !needwake && !timer_pending(&rtpcp->lazy_timer)) { | |
d119357d PM |
357 | if (rtp->lazy_jiffies) |
358 | mod_timer(&rtpcp->lazy_timer, rcu_tasks_lazy_time(rtp)); | |
359 | else | |
360 | needwake = rcu_segcblist_empty(&rtpcp->cblist); | |
cafafd67 | 361 | } |
d119357d PM |
362 | if (needwake) |
363 | rtpcp->urgent_gp = 3; | |
9b073de1 | 364 | rcu_segcblist_enqueue(&rtpcp->cblist, rhp); |
381a4f3b | 365 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); |
ab97152f PM |
366 | if (unlikely(needadjust)) { |
367 | raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); | |
368 | if (rtp->percpu_enqueue_lim != nr_cpu_ids) { | |
00a8b4b5 | 369 | WRITE_ONCE(rtp->percpu_enqueue_shift, 0); |
fd796e41 | 370 | WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids); |
ab97152f PM |
371 | smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids); |
372 | pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name); | |
373 | } | |
374 | raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); | |
375 | } | |
fd796e41 | 376 | rcu_read_unlock(); |
eacd6f04 | 377 | /* We can't create the thread unless interrupts are enabled. */ |
07e10515 | 378 | if (needwake && READ_ONCE(rtp->kthread_ptr)) |
3063b33a | 379 | irq_work_queue(&rtpcp->rtp_irq_work); |
eacd6f04 | 380 | } |
eacd6f04 | 381 | |
ce9b1c66 PM |
382 | // RCU callback function for rcu_barrier_tasks_generic(). |
383 | static void rcu_barrier_tasks_generic_cb(struct rcu_head *rhp) | |
384 | { | |
385 | struct rcu_tasks *rtp; | |
386 | struct rcu_tasks_percpu *rtpcp; | |
387 | ||
388 | rtpcp = container_of(rhp, struct rcu_tasks_percpu, barrier_q_head); | |
389 | rtp = rtpcp->rtpp; | |
390 | if (atomic_dec_and_test(&rtp->barrier_q_count)) | |
391 | complete(&rtp->barrier_q_completion); | |
392 | } | |
393 | ||
394 | // Wait for all in-flight callbacks for the specified RCU Tasks flavor. | |
395 | // Operates in a manner similar to rcu_barrier(). | |
396 | static void rcu_barrier_tasks_generic(struct rcu_tasks *rtp) | |
397 | { | |
398 | int cpu; | |
399 | unsigned long flags; | |
400 | struct rcu_tasks_percpu *rtpcp; | |
401 | unsigned long s = rcu_seq_snap(&rtp->barrier_q_seq); | |
402 | ||
403 | mutex_lock(&rtp->barrier_q_mutex); | |
404 | if (rcu_seq_done(&rtp->barrier_q_seq, s)) { | |
405 | smp_mb(); | |
406 | mutex_unlock(&rtp->barrier_q_mutex); | |
407 | return; | |
408 | } | |
409 | rcu_seq_start(&rtp->barrier_q_seq); | |
410 | init_completion(&rtp->barrier_q_completion); | |
411 | atomic_set(&rtp->barrier_q_count, 2); | |
412 | for_each_possible_cpu(cpu) { | |
2cee0789 | 413 | if (cpu >= smp_load_acquire(&rtp->percpu_dequeue_lim)) |
ce9b1c66 PM |
414 | break; |
415 | rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); | |
416 | rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb; | |
417 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
418 | if (rcu_segcblist_entrain(&rtpcp->cblist, &rtpcp->barrier_q_head)) | |
419 | atomic_inc(&rtp->barrier_q_count); | |
420 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
421 | } | |
422 | if (atomic_sub_and_test(2, &rtp->barrier_q_count)) | |
423 | complete(&rtp->barrier_q_completion); | |
424 | wait_for_completion(&rtp->barrier_q_completion); | |
425 | rcu_seq_end(&rtp->barrier_q_seq); | |
426 | mutex_unlock(&rtp->barrier_q_mutex); | |
427 | } | |
428 | ||
4d1114c0 PM |
429 | // Advance callbacks and indicate whether either a grace period or |
430 | // callback invocation is needed. | |
431 | static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) | |
432 | { | |
433 | int cpu; | |
e62d8ae4 | 434 | int dequeue_limit; |
4d1114c0 | 435 | unsigned long flags; |
a4fcfbee | 436 | bool gpdone = poll_state_synchronize_rcu(rtp->percpu_dequeue_gpseq); |
fd796e41 PM |
437 | long n; |
438 | long ncbs = 0; | |
439 | long ncbsnz = 0; | |
4d1114c0 PM |
440 | int needgpcb = 0; |
441 | ||
e62d8ae4 PM |
442 | dequeue_limit = smp_load_acquire(&rtp->percpu_dequeue_lim); |
443 | for (cpu = 0; cpu < dequeue_limit; cpu++) { | |
4d1114c0 PM |
444 | struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); |
445 | ||
446 | /* Advance and accelerate any new callbacks. */ | |
fd796e41 | 447 | if (!rcu_segcblist_n_cbs(&rtpcp->cblist)) |
4d1114c0 PM |
448 | continue; |
449 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
fd796e41 PM |
450 | // Should we shrink down to a single callback queue? |
451 | n = rcu_segcblist_n_cbs(&rtpcp->cblist); | |
452 | if (n) { | |
453 | ncbs += n; | |
454 | if (cpu > 0) | |
455 | ncbsnz += n; | |
456 | } | |
4d1114c0 PM |
457 | rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq)); |
458 | (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq)); | |
d119357d PM |
459 | if (rtpcp->urgent_gp > 0 && rcu_segcblist_pend_cbs(&rtpcp->cblist)) { |
460 | if (rtp->lazy_jiffies) | |
461 | rtpcp->urgent_gp--; | |
4d1114c0 | 462 | needgpcb |= 0x3; |
d119357d PM |
463 | } else if (rcu_segcblist_empty(&rtpcp->cblist)) { |
464 | rtpcp->urgent_gp = 0; | |
465 | } | |
466 | if (rcu_segcblist_ready_cbs(&rtpcp->cblist)) | |
4d1114c0 PM |
467 | needgpcb |= 0x1; |
468 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
469 | } | |
fd796e41 PM |
470 | |
471 | // Shrink down to a single callback queue if appropriate. | |
472 | // This is done in two stages: (1) If there are no more than | |
473 | // rcu_task_collapse_lim callbacks on CPU 0 and none on any other | |
474 | // CPU, limit enqueueing to CPU 0. (2) After an RCU grace period, | |
475 | // if there has not been an increase in callbacks, limit dequeuing | |
476 | // to CPU 0. Note the matching RCU read-side critical section in | |
477 | // call_rcu_tasks_generic(). | |
478 | if (rcu_task_cb_adjust && ncbs <= rcu_task_collapse_lim) { | |
479 | raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); | |
480 | if (rtp->percpu_enqueue_lim > 1) { | |
2bcd18e0 | 481 | WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids)); |
fd796e41 PM |
482 | smp_store_release(&rtp->percpu_enqueue_lim, 1); |
483 | rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu(); | |
a4fcfbee | 484 | gpdone = false; |
fd796e41 PM |
485 | pr_info("Starting switch %s to CPU-0 callback queuing.\n", rtp->name); |
486 | } | |
487 | raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); | |
488 | } | |
a4fcfbee | 489 | if (rcu_task_cb_adjust && !ncbsnz && gpdone) { |
fd796e41 PM |
490 | raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); |
491 | if (rtp->percpu_enqueue_lim < rtp->percpu_dequeue_lim) { | |
492 | WRITE_ONCE(rtp->percpu_dequeue_lim, 1); | |
493 | pr_info("Completing switch %s to CPU-0 callback queuing.\n", rtp->name); | |
494 | } | |
a4fcfbee Z |
495 | if (rtp->percpu_dequeue_lim == 1) { |
496 | for (cpu = rtp->percpu_dequeue_lim; cpu < nr_cpu_ids; cpu++) { | |
497 | struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); | |
4cf0585c | 498 | |
a4fcfbee Z |
499 | WARN_ON_ONCE(rcu_segcblist_n_cbs(&rtpcp->cblist)); |
500 | } | |
4cf0585c | 501 | } |
fd796e41 PM |
502 | raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); |
503 | } | |
504 | ||
4d1114c0 PM |
505 | return needgpcb; |
506 | } | |
507 | ||
57881863 | 508 | // Advance callbacks and invoke any that are ready. |
d363f833 | 509 | static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu *rtpcp) |
eacd6f04 | 510 | { |
57881863 | 511 | int cpu; |
d363f833 | 512 | int cpunext; |
401b0de3 | 513 | int cpuwq; |
eacd6f04 | 514 | unsigned long flags; |
9b073de1 | 515 | int len; |
9b073de1 | 516 | struct rcu_head *rhp; |
d363f833 PM |
517 | struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); |
518 | struct rcu_tasks_percpu *rtpcp_next; | |
519 | ||
520 | cpu = rtpcp->cpu; | |
521 | cpunext = cpu * 2 + 1; | |
2cee0789 | 522 | if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { |
d363f833 | 523 | rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); |
401b0de3 PM |
524 | cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; |
525 | queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); | |
d363f833 | 526 | cpunext++; |
2cee0789 | 527 | if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { |
d363f833 | 528 | rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); |
401b0de3 PM |
529 | cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; |
530 | queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); | |
57881863 | 531 | } |
57881863 | 532 | } |
d363f833 | 533 | |
ab2756ea | 534 | if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu)) |
d363f833 PM |
535 | return; |
536 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
537 | rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq)); | |
538 | rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl); | |
539 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
540 | len = rcl.len; | |
541 | for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) { | |
2cbc482d | 542 | debug_rcu_head_callback(rhp); |
d363f833 PM |
543 | local_bh_disable(); |
544 | rhp->func(rhp); | |
545 | local_bh_enable(); | |
546 | cond_resched(); | |
547 | } | |
548 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
549 | rcu_segcblist_add_len(&rtpcp->cblist, -len); | |
550 | (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq)); | |
551 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
552 | } | |
553 | ||
554 | // Workqueue flood to advance callbacks and invoke any that are ready. | |
555 | static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp) | |
556 | { | |
557 | struct rcu_tasks *rtp; | |
558 | struct rcu_tasks_percpu *rtpcp = container_of(wp, struct rcu_tasks_percpu, rtp_work); | |
559 | ||
560 | rtp = rtpcp->rtpp; | |
561 | rcu_tasks_invoke_cbs(rtp, rtpcp); | |
57881863 PM |
562 | } |
563 | ||
d96225fd | 564 | // Wait for one grace period. |
4a8cc433 | 565 | static void rcu_tasks_one_gp(struct rcu_tasks *rtp, bool midboot) |
57881863 PM |
566 | { |
567 | int needgpcb; | |
d96225fd PM |
568 | |
569 | mutex_lock(&rtp->tasks_gp_mutex); | |
d96225fd PM |
570 | |
571 | // If there were none, wait a bit and start over. | |
4a8cc433 PM |
572 | if (unlikely(midboot)) { |
573 | needgpcb = 0x2; | |
574 | } else { | |
9d0cce2b | 575 | mutex_unlock(&rtp->tasks_gp_mutex); |
4a8cc433 PM |
576 | set_tasks_gp_state(rtp, RTGS_WAIT_CBS); |
577 | rcuwait_wait_event(&rtp->cbs_wait, | |
578 | (needgpcb = rcu_tasks_need_gpcb(rtp)), | |
579 | TASK_IDLE); | |
9d0cce2b | 580 | mutex_lock(&rtp->tasks_gp_mutex); |
4a8cc433 | 581 | } |
d96225fd PM |
582 | |
583 | if (needgpcb & 0x2) { | |
584 | // Wait for one grace period. | |
585 | set_tasks_gp_state(rtp, RTGS_WAIT_GP); | |
586 | rtp->gp_start = jiffies; | |
587 | rcu_seq_start(&rtp->tasks_gp_seq); | |
588 | rtp->gp_func(rtp); | |
589 | rcu_seq_end(&rtp->tasks_gp_seq); | |
590 | } | |
591 | ||
592 | // Invoke callbacks. | |
593 | set_tasks_gp_state(rtp, RTGS_INVOKE_CBS); | |
594 | rcu_tasks_invoke_cbs(rtp, per_cpu_ptr(rtp->rtpcpu, 0)); | |
595 | mutex_unlock(&rtp->tasks_gp_mutex); | |
596 | } | |
597 | ||
598 | // RCU-tasks kthread that detects grace periods and invokes callbacks. | |
599 | static int __noreturn rcu_tasks_kthread(void *arg) | |
600 | { | |
d119357d | 601 | int cpu; |
07e10515 | 602 | struct rcu_tasks *rtp = arg; |
eacd6f04 | 603 | |
d119357d PM |
604 | for_each_possible_cpu(cpu) { |
605 | struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); | |
606 | ||
607 | timer_setup(&rtpcp->lazy_timer, call_rcu_tasks_generic_timer, 0); | |
608 | rtpcp->urgent_gp = 1; | |
609 | } | |
610 | ||
eacd6f04 | 611 | /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ |
04d4e665 | 612 | housekeeping_affine(current, HK_TYPE_RCU); |
d119357d | 613 | smp_store_release(&rtp->kthread_ptr, current); // Let GPs start! |
eacd6f04 PM |
614 | |
615 | /* | |
616 | * Each pass through the following loop makes one check for | |
617 | * newly arrived callbacks, and, if there are some, waits for | |
618 | * one RCU-tasks grace period and then invokes the callbacks. | |
619 | * This loop is terminated by the system going down. ;-) | |
620 | */ | |
621 | for (;;) { | |
d96225fd PM |
622 | // Wait for one grace period and invoke any callbacks |
623 | // that are ready. | |
4a8cc433 | 624 | rcu_tasks_one_gp(rtp, false); |
57881863 | 625 | |
d96225fd | 626 | // Paranoid sleep to keep this from entering a tight loop. |
4fe192df | 627 | schedule_timeout_idle(rtp->gp_sleep); |
eacd6f04 PM |
628 | } |
629 | } | |
630 | ||
68cb4720 PM |
631 | // Wait for a grace period for the specified flavor of Tasks RCU. |
632 | static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp) | |
633 | { | |
634 | /* Complain if the scheduler has not started. */ | |
ea5c8987 Z |
635 | if (WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, |
636 | "synchronize_%s() called too soon", rtp->name)) | |
637 | return; | |
68cb4720 | 638 | |
4a8cc433 PM |
639 | // If the grace-period kthread is running, use it. |
640 | if (READ_ONCE(rtp->kthread_ptr)) { | |
641 | wait_rcu_gp(rtp->call_func); | |
642 | return; | |
643 | } | |
644 | rcu_tasks_one_gp(rtp, true); | |
68cb4720 PM |
645 | } |
646 | ||
1b04fa99 | 647 | /* Spawn RCU-tasks grace-period kthread. */ |
5873b8a9 | 648 | static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp) |
eacd6f04 PM |
649 | { |
650 | struct task_struct *t; | |
651 | ||
c97d12a6 PM |
652 | t = kthread_run(rcu_tasks_kthread, rtp, "%s_kthread", rtp->kname); |
653 | if (WARN_ONCE(IS_ERR(t), "%s: Could not start %s grace-period kthread, OOM is now expected behavior\n", __func__, rtp->name)) | |
5873b8a9 | 654 | return; |
eacd6f04 | 655 | smp_mb(); /* Ensure others see full kthread. */ |
eacd6f04 | 656 | } |
eacd6f04 | 657 | |
eacd6f04 PM |
658 | #ifndef CONFIG_TINY_RCU |
659 | ||
660 | /* | |
661 | * Print any non-default Tasks RCU settings. | |
662 | */ | |
663 | static void __init rcu_tasks_bootup_oddness(void) | |
664 | { | |
d5f177d3 | 665 | #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) |
f2539003 PM |
666 | int rtsimc; |
667 | ||
eacd6f04 PM |
668 | if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT) |
669 | pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout); | |
f2539003 PM |
670 | rtsimc = clamp(rcu_task_stall_info_mult, 1, 10); |
671 | if (rtsimc != rcu_task_stall_info_mult) { | |
672 | pr_info("\tTasks-RCU CPU stall info multiplier clamped to %d (rcu_task_stall_info_mult).\n", rtsimc); | |
673 | rcu_task_stall_info_mult = rtsimc; | |
674 | } | |
d5f177d3 PM |
675 | #endif /* #ifdef CONFIG_TASKS_RCU */ |
676 | #ifdef CONFIG_TASKS_RCU | |
677 | pr_info("\tTrampoline variant of Tasks RCU enabled.\n"); | |
eacd6f04 | 678 | #endif /* #ifdef CONFIG_TASKS_RCU */ |
c84aad76 PM |
679 | #ifdef CONFIG_TASKS_RUDE_RCU |
680 | pr_info("\tRude variant of Tasks RCU enabled.\n"); | |
681 | #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ | |
d5f177d3 PM |
682 | #ifdef CONFIG_TASKS_TRACE_RCU |
683 | pr_info("\tTracing variant of Tasks RCU enabled.\n"); | |
684 | #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ | |
eacd6f04 PM |
685 | } |
686 | ||
687 | #endif /* #ifndef CONFIG_TINY_RCU */ | |
5873b8a9 | 688 | |
8344496e | 689 | #ifndef CONFIG_TINY_RCU |
e21408ce PM |
690 | /* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */ |
691 | static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) | |
692 | { | |
10b3742f PM |
693 | int cpu; |
694 | bool havecbs = false; | |
d119357d PM |
695 | bool haveurgent = false; |
696 | bool haveurgentcbs = false; | |
10b3742f PM |
697 | |
698 | for_each_possible_cpu(cpu) { | |
699 | struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); | |
700 | ||
d119357d | 701 | if (!data_race(rcu_segcblist_empty(&rtpcp->cblist))) |
10b3742f | 702 | havecbs = true; |
d119357d PM |
703 | if (data_race(rtpcp->urgent_gp)) |
704 | haveurgent = true; | |
705 | if (!data_race(rcu_segcblist_empty(&rtpcp->cblist)) && data_race(rtpcp->urgent_gp)) | |
706 | haveurgentcbs = true; | |
707 | if (havecbs && haveurgent && haveurgentcbs) | |
10b3742f | 708 | break; |
10b3742f | 709 | } |
d119357d | 710 | pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c%c%c l:%lu %s\n", |
e21408ce | 711 | rtp->kname, |
7e0669c3 | 712 | tasks_gp_state_getname(rtp), data_race(rtp->gp_state), |
af051ca4 | 713 | jiffies - data_race(rtp->gp_jiffies), |
b14fb4fb | 714 | data_race(rcu_seq_current(&rtp->tasks_gp_seq)), |
7e0669c3 | 715 | data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis), |
e21408ce | 716 | ".k"[!!data_race(rtp->kthread_ptr)], |
10b3742f | 717 | ".C"[havecbs], |
d119357d PM |
718 | ".u"[haveurgent], |
719 | ".U"[haveurgentcbs], | |
720 | rtp->lazy_jiffies, | |
e21408ce PM |
721 | s); |
722 | } | |
27c0f144 | 723 | #endif // #ifndef CONFIG_TINY_RCU |
e21408ce | 724 | |
25246fc8 PM |
725 | static void exit_tasks_rcu_finish_trace(struct task_struct *t); |
726 | ||
727 | #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) | |
5873b8a9 | 728 | |
d01aa263 PM |
729 | //////////////////////////////////////////////////////////////////////// |
730 | // | |
731 | // Shared code between task-list-scanning variants of Tasks RCU. | |
732 | ||
733 | /* Wait for one RCU-tasks grace period. */ | |
734 | static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) | |
735 | { | |
f2539003 | 736 | struct task_struct *g; |
d01aa263 | 737 | int fract; |
f2539003 PM |
738 | LIST_HEAD(holdouts); |
739 | unsigned long j; | |
740 | unsigned long lastinfo; | |
741 | unsigned long lastreport; | |
742 | bool reported = false; | |
743 | int rtsi; | |
744 | struct task_struct *t; | |
d01aa263 | 745 | |
af051ca4 | 746 | set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP); |
7460ade1 | 747 | rtp->pregp_func(&holdouts); |
d01aa263 PM |
748 | |
749 | /* | |
750 | * There were callbacks, so we need to wait for an RCU-tasks | |
751 | * grace period. Start off by scanning the task list for tasks | |
752 | * that are not already voluntarily blocked. Mark these tasks | |
753 | * and make a list of them in holdouts. | |
754 | */ | |
af051ca4 | 755 | set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST); |
1a4a8153 PM |
756 | if (rtp->pertask_func) { |
757 | rcu_read_lock(); | |
758 | for_each_process_thread(g, t) | |
759 | rtp->pertask_func(t, &holdouts); | |
760 | rcu_read_unlock(); | |
761 | } | |
d01aa263 | 762 | |
af051ca4 | 763 | set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST); |
9796e1ae | 764 | rtp->postscan_func(&holdouts); |
d01aa263 PM |
765 | |
766 | /* | |
767 | * Each pass through the following loop scans the list of holdout | |
768 | * tasks, removing any that are no longer holdouts. When the list | |
769 | * is empty, we are done. | |
770 | */ | |
771 | lastreport = jiffies; | |
f2539003 PM |
772 | lastinfo = lastreport; |
773 | rtsi = READ_ONCE(rcu_task_stall_info); | |
d01aa263 | 774 | |
2393a613 PM |
775 | // Start off with initial wait and slowly back off to 1 HZ wait. |
776 | fract = rtp->init_fract; | |
d01aa263 | 777 | |
77dc1741 | 778 | while (!list_empty(&holdouts)) { |
777570d9 | 779 | ktime_t exp; |
d01aa263 PM |
780 | bool firstreport; |
781 | bool needreport; | |
782 | int rtst; | |
783 | ||
f2539003 | 784 | // Slowly back off waiting for holdouts |
af051ca4 | 785 | set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS); |
bddf7122 PM |
786 | if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { |
787 | schedule_timeout_idle(fract); | |
788 | } else { | |
789 | exp = jiffies_to_nsecs(fract); | |
790 | __set_current_state(TASK_IDLE); | |
791 | schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD); | |
792 | } | |
d01aa263 | 793 | |
75dc2da5 PM |
794 | if (fract < HZ) |
795 | fract++; | |
d01aa263 PM |
796 | |
797 | rtst = READ_ONCE(rcu_task_stall_timeout); | |
798 | needreport = rtst > 0 && time_after(jiffies, lastreport + rtst); | |
f2539003 | 799 | if (needreport) { |
d01aa263 | 800 | lastreport = jiffies; |
f2539003 PM |
801 | reported = true; |
802 | } | |
d01aa263 PM |
803 | firstreport = true; |
804 | WARN_ON(signal_pending(current)); | |
af051ca4 | 805 | set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS); |
d01aa263 | 806 | rtp->holdouts_func(&holdouts, needreport, &firstreport); |
f2539003 PM |
807 | |
808 | // Print pre-stall informational messages if needed. | |
809 | j = jiffies; | |
810 | if (rtsi > 0 && !reported && time_after(j, lastinfo + rtsi)) { | |
811 | lastinfo = j; | |
812 | rtsi = rtsi * rcu_task_stall_info_mult; | |
df83fff7 | 813 | pr_info("%s: %s grace period number %lu (since boot) is %lu jiffies old.\n", |
f2539003 PM |
814 | __func__, rtp->kname, rtp->tasks_gp_seq, j - rtp->gp_start); |
815 | } | |
d01aa263 PM |
816 | } |
817 | ||
af051ca4 PM |
818 | set_tasks_gp_state(rtp, RTGS_POST_GP); |
819 | rtp->postgp_func(rtp); | |
d01aa263 PM |
820 | } |
821 | ||
25246fc8 PM |
822 | #endif /* #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) */ |
823 | ||
824 | #ifdef CONFIG_TASKS_RCU | |
825 | ||
5873b8a9 PM |
826 | //////////////////////////////////////////////////////////////////////// |
827 | // | |
828 | // Simple variant of RCU whose quiescent states are voluntary context | |
8af9e2c7 | 829 | // switch, cond_resched_tasks_rcu_qs(), user-space execution, and idle. |
5873b8a9 PM |
830 | // As such, grace periods can take one good long time. There are no |
831 | // read-side primitives similar to rcu_read_lock() and rcu_read_unlock() | |
832 | // because this implementation is intended to get the system into a safe | |
833 | // state for some of the manipulations involved in tracing and the like. | |
834 | // Finally, this implementation does not support high call_rcu_tasks() | |
835 | // rates from multiple CPUs. If this is required, per-CPU callback lists | |
836 | // will be needed. | |
06a3ec92 PM |
837 | // |
838 | // The implementation uses rcu_tasks_wait_gp(), which relies on function | |
839 | // pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread() | |
840 | // function sets these function pointers up so that rcu_tasks_wait_gp() | |
841 | // invokes these functions in this order: | |
842 | // | |
843 | // rcu_tasks_pregp_step(): | |
844 | // Invokes synchronize_rcu() in order to wait for all in-flight | |
845 | // t->on_rq and t->nvcsw transitions to complete. This works because | |
846 | // all such transitions are carried out with interrupts disabled. | |
847 | // rcu_tasks_pertask(), invoked on every non-idle task: | |
848 | // For every runnable non-idle task other than the current one, use | |
849 | // get_task_struct() to pin down that task, snapshot that task's | |
850 | // number of voluntary context switches, and add that task to the | |
851 | // holdout list. | |
852 | // rcu_tasks_postscan(): | |
1612160b PM |
853 | // Gather per-CPU lists of tasks in do_exit() to ensure that all |
854 | // tasks that were in the process of exiting (and which thus might | |
855 | // not know to synchronize with this RCU Tasks grace period) have | |
856 | // completed exiting. The synchronize_rcu() in rcu_tasks_postgp() | |
857 | // will take care of any tasks stuck in the non-preemptible region | |
858 | // of do_exit() following its call to exit_tasks_rcu_stop(). | |
06a3ec92 PM |
859 | // check_all_holdout_tasks(), repeatedly until holdout list is empty: |
860 | // Scans the holdout list, attempting to identify a quiescent state | |
861 | // for each task on the list. If there is a quiescent state, the | |
862 | // corresponding task is removed from the holdout list. | |
863 | // rcu_tasks_postgp(): | |
864 | // Invokes synchronize_rcu() in order to ensure that all prior | |
865 | // t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks | |
866 | // to have happened before the end of this RCU Tasks grace period. | |
867 | // Again, this works because all such transitions are carried out | |
868 | // with interrupts disabled. | |
869 | // | |
870 | // For each exiting task, the exit_tasks_rcu_start() and | |
1612160b PM |
871 | // exit_tasks_rcu_finish() functions add and remove, respectively, the |
872 | // current task to a per-CPU list of tasks that rcu_tasks_postscan() must | |
873 | // wait on. This is necessary because rcu_tasks_postscan() must wait on | |
874 | // tasks that have already been removed from the global list of tasks. | |
06a3ec92 | 875 | // |
381a4f3b PM |
876 | // Pre-grace-period update-side code is ordered before the grace |
877 | // via the raw_spin_lock.*rcu_node(). Pre-grace-period read-side code | |
878 | // is ordered before the grace period via synchronize_rcu() call in | |
879 | // rcu_tasks_pregp_step() and by the scheduler's locks and interrupt | |
06a3ec92 | 880 | // disabling. |
5873b8a9 | 881 | |
e4fe5dd6 | 882 | /* Pre-grace-period preparation. */ |
7460ade1 | 883 | static void rcu_tasks_pregp_step(struct list_head *hop) |
e4fe5dd6 PM |
884 | { |
885 | /* | |
886 | * Wait for all pre-existing t->on_rq and t->nvcsw transitions | |
887 | * to complete. Invoking synchronize_rcu() suffices because all | |
888 | * these transitions occur with interrupts disabled. Without this | |
889 | * synchronize_rcu(), a read-side critical section that started | |
890 | * before the grace period might be incorrectly seen as having | |
891 | * started after the grace period. | |
892 | * | |
893 | * This synchronize_rcu() also dispenses with the need for a | |
894 | * memory barrier on the first store to t->rcu_tasks_holdout, | |
895 | * as it forces the store to happen after the beginning of the | |
896 | * grace period. | |
897 | */ | |
898 | synchronize_rcu(); | |
899 | } | |
900 | ||
9715ed50 FW |
901 | /* Check for quiescent states since the pregp's synchronize_rcu() */ |
902 | static bool rcu_tasks_is_holdout(struct task_struct *t) | |
903 | { | |
904 | int cpu; | |
905 | ||
906 | /* Has the task been seen voluntarily sleeping? */ | |
907 | if (!READ_ONCE(t->on_rq)) | |
908 | return false; | |
909 | ||
910 | /* | |
911 | * Idle tasks (or idle injection) within the idle loop are RCU-tasks | |
912 | * quiescent states. But CPU boot code performed by the idle task | |
913 | * isn't a quiescent state. | |
914 | */ | |
915 | if (is_idle_task(t)) | |
916 | return false; | |
917 | ||
918 | cpu = task_cpu(t); | |
919 | ||
920 | /* Idle tasks on offline CPUs are RCU-tasks quiescent states. */ | |
921 | if (t == idle_task(cpu) && !rcu_cpu_online(cpu)) | |
922 | return false; | |
923 | ||
924 | return true; | |
925 | } | |
926 | ||
e4fe5dd6 PM |
927 | /* Per-task initial processing. */ |
928 | static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) | |
929 | { | |
9715ed50 | 930 | if (t != current && rcu_tasks_is_holdout(t)) { |
e4fe5dd6 PM |
931 | get_task_struct(t); |
932 | t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); | |
933 | WRITE_ONCE(t->rcu_tasks_holdout, true); | |
934 | list_add(&t->rcu_tasks_holdout_list, hop); | |
935 | } | |
936 | } | |
937 | ||
1612160b PM |
938 | void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func); |
939 | DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks"); | |
940 | ||
e4fe5dd6 | 941 | /* Processing between scanning taskslist and draining the holdout list. */ |
04a3c5aa | 942 | static void rcu_tasks_postscan(struct list_head *hop) |
e4fe5dd6 | 943 | { |
1612160b | 944 | int cpu; |
a4533cc0 NU |
945 | int rtsi = READ_ONCE(rcu_task_stall_info); |
946 | ||
947 | if (!IS_ENABLED(CONFIG_TINY_RCU)) { | |
948 | tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi; | |
949 | add_timer(&tasks_rcu_exit_srcu_stall_timer); | |
950 | } | |
951 | ||
e4fe5dd6 | 952 | /* |
e4e1e808 FW |
953 | * Exiting tasks may escape the tasklist scan. Those are vulnerable |
954 | * until their final schedule() with TASK_DEAD state. To cope with | |
955 | * this, divide the fragile exit path part in two intersecting | |
956 | * read side critical sections: | |
957 | * | |
1612160b PM |
958 | * 1) A task_struct list addition before calling exit_notify(), |
959 | * which may remove the task from the tasklist, with the | |
960 | * removal after the final preempt_disable() call in do_exit(). | |
e4e1e808 FW |
961 | * |
962 | * 2) An _RCU_ read side starting with the final preempt_disable() | |
963 | * call in do_exit() and ending with the final call to schedule() | |
964 | * with TASK_DEAD state. | |
965 | * | |
966 | * This handles the part 1). And postgp will handle part 2) with a | |
967 | * call to synchronize_rcu(). | |
e4fe5dd6 | 968 | */ |
1612160b PM |
969 | |
970 | for_each_possible_cpu(cpu) { | |
0bb11a37 | 971 | unsigned long j = jiffies + 1; |
1612160b PM |
972 | struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, cpu); |
973 | struct task_struct *t; | |
0bb11a37 PM |
974 | struct task_struct *t1; |
975 | struct list_head tmp; | |
1612160b PM |
976 | |
977 | raw_spin_lock_irq_rcu_node(rtpcp); | |
0bb11a37 | 978 | list_for_each_entry_safe(t, t1, &rtpcp->rtp_exit_list, rcu_tasks_exit_list) { |
1612160b PM |
979 | if (list_empty(&t->rcu_tasks_holdout_list)) |
980 | rcu_tasks_pertask(t, hop); | |
0bb11a37 PM |
981 | |
982 | // RT kernels need frequent pauses, otherwise | |
983 | // pause at least once per pair of jiffies. | |
984 | if (!IS_ENABLED(CONFIG_PREEMPT_RT) && time_before(jiffies, j)) | |
985 | continue; | |
986 | ||
987 | // Keep our place in the list while pausing. | |
988 | // Nothing else traverses this list, so adding a | |
989 | // bare list_head is OK. | |
990 | list_add(&tmp, &t->rcu_tasks_exit_list); | |
991 | raw_spin_unlock_irq_rcu_node(rtpcp); | |
992 | cond_resched(); // For CONFIG_PREEMPT=n kernels | |
993 | raw_spin_lock_irq_rcu_node(rtpcp); | |
994 | t1 = list_entry(tmp.next, struct task_struct, rcu_tasks_exit_list); | |
995 | list_del(&tmp); | |
996 | j = jiffies + 1; | |
997 | } | |
1612160b PM |
998 | raw_spin_unlock_irq_rcu_node(rtpcp); |
999 | } | |
a4533cc0 NU |
1000 | |
1001 | if (!IS_ENABLED(CONFIG_TINY_RCU)) | |
1002 | del_timer_sync(&tasks_rcu_exit_srcu_stall_timer); | |
e4fe5dd6 PM |
1003 | } |
1004 | ||
5873b8a9 PM |
1005 | /* See if tasks are still holding out, complain if so. */ |
1006 | static void check_holdout_task(struct task_struct *t, | |
1007 | bool needreport, bool *firstreport) | |
1008 | { | |
1009 | int cpu; | |
1010 | ||
1011 | if (!READ_ONCE(t->rcu_tasks_holdout) || | |
1012 | t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || | |
9715ed50 | 1013 | !rcu_tasks_is_holdout(t) || |
5873b8a9 | 1014 | (IS_ENABLED(CONFIG_NO_HZ_FULL) && |
18966f7b | 1015 | !is_idle_task(t) && READ_ONCE(t->rcu_tasks_idle_cpu) >= 0)) { |
5873b8a9 PM |
1016 | WRITE_ONCE(t->rcu_tasks_holdout, false); |
1017 | list_del_init(&t->rcu_tasks_holdout_list); | |
1018 | put_task_struct(t); | |
1019 | return; | |
1020 | } | |
1021 | rcu_request_urgent_qs_task(t); | |
1022 | if (!needreport) | |
1023 | return; | |
1024 | if (*firstreport) { | |
1025 | pr_err("INFO: rcu_tasks detected stalls on tasks:\n"); | |
1026 | *firstreport = false; | |
1027 | } | |
1028 | cpu = task_cpu(t); | |
1029 | pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n", | |
1030 | t, ".I"[is_idle_task(t)], | |
1031 | "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], | |
1032 | t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, | |
18966f7b | 1033 | data_race(t->rcu_tasks_idle_cpu), cpu); |
5873b8a9 PM |
1034 | sched_show_task(t); |
1035 | } | |
1036 | ||
e4fe5dd6 PM |
1037 | /* Scan the holdout lists for tasks no longer holding out. */ |
1038 | static void check_all_holdout_tasks(struct list_head *hop, | |
1039 | bool needreport, bool *firstreport) | |
1040 | { | |
1041 | struct task_struct *t, *t1; | |
1042 | ||
1043 | list_for_each_entry_safe(t, t1, hop, rcu_tasks_holdout_list) { | |
1044 | check_holdout_task(t, needreport, firstreport); | |
1045 | cond_resched(); | |
1046 | } | |
1047 | } | |
1048 | ||
1049 | /* Finish off the Tasks-RCU grace period. */ | |
af051ca4 | 1050 | static void rcu_tasks_postgp(struct rcu_tasks *rtp) |
e4fe5dd6 PM |
1051 | { |
1052 | /* | |
1053 | * Because ->on_rq and ->nvcsw are not guaranteed to have a full | |
1054 | * memory barriers prior to them in the schedule() path, memory | |
1055 | * reordering on other CPUs could cause their RCU-tasks read-side | |
1056 | * critical sections to extend past the end of the grace period. | |
1057 | * However, because these ->nvcsw updates are carried out with | |
1058 | * interrupts disabled, we can use synchronize_rcu() to force the | |
1059 | * needed ordering on all such CPUs. | |
1060 | * | |
1061 | * This synchronize_rcu() also confines all ->rcu_tasks_holdout | |
1062 | * accesses to be within the grace period, avoiding the need for | |
1063 | * memory barriers for ->rcu_tasks_holdout accesses. | |
1064 | * | |
1065 | * In addition, this synchronize_rcu() waits for exiting tasks | |
1066 | * to complete their final preempt_disable() region of execution, | |
e4e1e808 FW |
1067 | * enforcing the whole region before tasklist removal until |
1068 | * the final schedule() with TASK_DEAD state to be an RCU TASKS | |
1069 | * read side critical section. | |
e4fe5dd6 PM |
1070 | */ |
1071 | synchronize_rcu(); | |
1072 | } | |
1073 | ||
a4533cc0 NU |
1074 | static void tasks_rcu_exit_srcu_stall(struct timer_list *unused) |
1075 | { | |
1076 | #ifndef CONFIG_TINY_RCU | |
1077 | int rtsi; | |
1078 | ||
1079 | rtsi = READ_ONCE(rcu_task_stall_info); | |
1080 | pr_info("%s: %s grace period number %lu (since boot) gp_state: %s is %lu jiffies old.\n", | |
1081 | __func__, rcu_tasks.kname, rcu_tasks.tasks_gp_seq, | |
1082 | tasks_gp_state_getname(&rcu_tasks), jiffies - rcu_tasks.gp_jiffies); | |
1083 | pr_info("Please check any exiting tasks stuck between calls to exit_tasks_rcu_start() and exit_tasks_rcu_finish()\n"); | |
1084 | tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi; | |
1085 | add_timer(&tasks_rcu_exit_srcu_stall_timer); | |
1086 | #endif // #ifndef CONFIG_TINY_RCU | |
1087 | } | |
1088 | ||
5873b8a9 PM |
1089 | /** |
1090 | * call_rcu_tasks() - Queue an RCU for invocation task-based grace period | |
1091 | * @rhp: structure to be used for queueing the RCU updates. | |
1092 | * @func: actual callback function to be invoked after the grace period | |
1093 | * | |
1094 | * The callback function will be invoked some time after a full grace | |
1095 | * period elapses, in other words after all currently executing RCU | |
1096 | * read-side critical sections have completed. call_rcu_tasks() assumes | |
1097 | * that the read-side critical sections end at a voluntary context | |
8af9e2c7 | 1098 | * switch (not a preemption!), cond_resched_tasks_rcu_qs(), entry into idle, |
5873b8a9 PM |
1099 | * or transition to usermode execution. As such, there are no read-side |
1100 | * primitives analogous to rcu_read_lock() and rcu_read_unlock() because | |
1101 | * this primitive is intended to determine that all tasks have passed | |
a616aec9 | 1102 | * through a safe state, not so much for data-structure synchronization. |
5873b8a9 PM |
1103 | * |
1104 | * See the description of call_rcu() for more detailed information on | |
1105 | * memory ordering guarantees. | |
1106 | */ | |
1107 | void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) | |
1108 | { | |
1109 | call_rcu_tasks_generic(rhp, func, &rcu_tasks); | |
1110 | } | |
1111 | EXPORT_SYMBOL_GPL(call_rcu_tasks); | |
1112 | ||
1113 | /** | |
1114 | * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. | |
1115 | * | |
1116 | * Control will return to the caller some time after a full rcu-tasks | |
1117 | * grace period has elapsed, in other words after all currently | |
1118 | * executing rcu-tasks read-side critical sections have elapsed. These | |
1119 | * read-side critical sections are delimited by calls to schedule(), | |
1120 | * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls | |
1121 | * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). | |
1122 | * | |
1123 | * This is a very specialized primitive, intended only for a few uses in | |
1124 | * tracing and other situations requiring manipulation of function | |
1125 | * preambles and profiling hooks. The synchronize_rcu_tasks() function | |
1126 | * is not (yet) intended for heavy use from multiple CPUs. | |
1127 | * | |
1128 | * See the description of synchronize_rcu() for more detailed information | |
1129 | * on memory ordering guarantees. | |
1130 | */ | |
1131 | void synchronize_rcu_tasks(void) | |
1132 | { | |
1133 | synchronize_rcu_tasks_generic(&rcu_tasks); | |
1134 | } | |
1135 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); | |
1136 | ||
1137 | /** | |
1138 | * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. | |
1139 | * | |
1140 | * Although the current implementation is guaranteed to wait, it is not | |
1141 | * obligated to, for example, if there are no pending callbacks. | |
1142 | */ | |
1143 | void rcu_barrier_tasks(void) | |
1144 | { | |
ce9b1c66 | 1145 | rcu_barrier_tasks_generic(&rcu_tasks); |
5873b8a9 PM |
1146 | } |
1147 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks); | |
1148 | ||
0325e8a1 | 1149 | static int rcu_tasks_lazy_ms = -1; |
450d461a PM |
1150 | module_param(rcu_tasks_lazy_ms, int, 0444); |
1151 | ||
5873b8a9 PM |
1152 | static int __init rcu_spawn_tasks_kthread(void) |
1153 | { | |
4fe192df | 1154 | rcu_tasks.gp_sleep = HZ / 10; |
75dc2da5 | 1155 | rcu_tasks.init_fract = HZ / 10; |
450d461a PM |
1156 | if (rcu_tasks_lazy_ms >= 0) |
1157 | rcu_tasks.lazy_jiffies = msecs_to_jiffies(rcu_tasks_lazy_ms); | |
e4fe5dd6 PM |
1158 | rcu_tasks.pregp_func = rcu_tasks_pregp_step; |
1159 | rcu_tasks.pertask_func = rcu_tasks_pertask; | |
1160 | rcu_tasks.postscan_func = rcu_tasks_postscan; | |
1161 | rcu_tasks.holdouts_func = check_all_holdout_tasks; | |
1162 | rcu_tasks.postgp_func = rcu_tasks_postgp; | |
5873b8a9 PM |
1163 | rcu_spawn_tasks_kthread_generic(&rcu_tasks); |
1164 | return 0; | |
1165 | } | |
5873b8a9 | 1166 | |
27c0f144 PM |
1167 | #if !defined(CONFIG_TINY_RCU) |
1168 | void show_rcu_tasks_classic_gp_kthread(void) | |
e21408ce PM |
1169 | { |
1170 | show_rcu_tasks_generic_gp_kthread(&rcu_tasks, ""); | |
1171 | } | |
27c0f144 PM |
1172 | EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread); |
1173 | #endif // !defined(CONFIG_TINY_RCU) | |
e21408ce | 1174 | |
271a8467 PM |
1175 | struct task_struct *get_rcu_tasks_gp_kthread(void) |
1176 | { | |
1177 | return rcu_tasks.kthread_ptr; | |
1178 | } | |
1179 | EXPORT_SYMBOL_GPL(get_rcu_tasks_gp_kthread); | |
1180 | ||
e4e1e808 | 1181 | /* |
6b70399f PM |
1182 | * Protect against tasklist scan blind spot while the task is exiting and |
1183 | * may be removed from the tasklist. Do this by adding the task to yet | |
1184 | * another list. | |
1185 | * | |
1186 | * Note that the task will remove itself from this list, so there is no | |
1187 | * need for get_task_struct(), except in the case where rcu_tasks_pertask() | |
1188 | * adds it to the holdout list, in which case rcu_tasks_pertask() supplies | |
1189 | * the needed get_task_struct(). | |
e4e1e808 | 1190 | */ |
6b70399f | 1191 | void exit_tasks_rcu_start(void) |
25246fc8 | 1192 | { |
6b70399f PM |
1193 | unsigned long flags; |
1194 | struct rcu_tasks_percpu *rtpcp; | |
1195 | struct task_struct *t = current; | |
1196 | ||
1197 | WARN_ON_ONCE(!list_empty(&t->rcu_tasks_exit_list)); | |
1198 | preempt_disable(); | |
1199 | rtpcp = this_cpu_ptr(rcu_tasks.rtpcpu); | |
1200 | t->rcu_tasks_exit_cpu = smp_processor_id(); | |
1201 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
1202 | if (!rtpcp->rtp_exit_list.next) | |
1203 | INIT_LIST_HEAD(&rtpcp->rtp_exit_list); | |
1204 | list_add(&t->rcu_tasks_exit_list, &rtpcp->rtp_exit_list); | |
1205 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
1206 | preempt_enable(); | |
25246fc8 PM |
1207 | } |
1208 | ||
e4e1e808 | 1209 | /* |
6b70399f PM |
1210 | * Remove the task from the "yet another list" because do_exit() is now |
1211 | * non-preemptible, allowing synchronize_rcu() to wait beyond this point. | |
e4e1e808 | 1212 | */ |
6b70399f | 1213 | void exit_tasks_rcu_stop(void) |
25246fc8 | 1214 | { |
6b70399f PM |
1215 | unsigned long flags; |
1216 | struct rcu_tasks_percpu *rtpcp; | |
25246fc8 PM |
1217 | struct task_struct *t = current; |
1218 | ||
6b70399f PM |
1219 | WARN_ON_ONCE(list_empty(&t->rcu_tasks_exit_list)); |
1220 | rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, t->rcu_tasks_exit_cpu); | |
1221 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
1222 | list_del_init(&t->rcu_tasks_exit_list); | |
1223 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
28319d6d FW |
1224 | } |
1225 | ||
1226 | /* | |
1227 | * Contribute to protect against tasklist scan blind spot while the | |
1228 | * task is exiting and may be removed from the tasklist. See | |
1229 | * corresponding synchronize_srcu() for further details. | |
1230 | */ | |
1231 | void exit_tasks_rcu_finish(void) | |
1232 | { | |
1233 | exit_tasks_rcu_stop(); | |
1234 | exit_tasks_rcu_finish_trace(current); | |
25246fc8 PM |
1235 | } |
1236 | ||
e21408ce | 1237 | #else /* #ifdef CONFIG_TASKS_RCU */ |
25246fc8 | 1238 | void exit_tasks_rcu_start(void) { } |
28319d6d | 1239 | void exit_tasks_rcu_stop(void) { } |
25246fc8 | 1240 | void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); } |
e21408ce | 1241 | #endif /* #else #ifdef CONFIG_TASKS_RCU */ |
c84aad76 PM |
1242 | |
1243 | #ifdef CONFIG_TASKS_RUDE_RCU | |
1244 | ||
1245 | //////////////////////////////////////////////////////////////////////// | |
1246 | // | |
1247 | // "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of | |
1248 | // passing an empty function to schedule_on_each_cpu(). This approach | |
e4be1f44 PM |
1249 | // provides an asynchronous call_rcu_tasks_rude() API and batching of |
1250 | // concurrent calls to the synchronous synchronize_rcu_tasks_rude() API. | |
9fc98e31 PM |
1251 | // This invokes schedule_on_each_cpu() in order to send IPIs far and wide |
1252 | // and induces otherwise unnecessary context switches on all online CPUs, | |
1253 | // whether idle or not. | |
1254 | // | |
1255 | // Callback handling is provided by the rcu_tasks_kthread() function. | |
1256 | // | |
1257 | // Ordering is provided by the scheduler's context-switch code. | |
c84aad76 PM |
1258 | |
1259 | // Empty function to allow workqueues to force a context switch. | |
1260 | static void rcu_tasks_be_rude(struct work_struct *work) | |
1261 | { | |
1262 | } | |
1263 | ||
1264 | // Wait for one rude RCU-tasks grace period. | |
1265 | static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp) | |
1266 | { | |
238dbce3 | 1267 | rtp->n_ipis += cpumask_weight(cpu_online_mask); |
c84aad76 PM |
1268 | schedule_on_each_cpu(rcu_tasks_be_rude); |
1269 | } | |
1270 | ||
1271 | void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func); | |
c97d12a6 PM |
1272 | DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude, |
1273 | "RCU Tasks Rude"); | |
c84aad76 PM |
1274 | |
1275 | /** | |
1276 | * call_rcu_tasks_rude() - Queue a callback rude task-based grace period | |
1277 | * @rhp: structure to be used for queueing the RCU updates. | |
1278 | * @func: actual callback function to be invoked after the grace period | |
1279 | * | |
1280 | * The callback function will be invoked some time after a full grace | |
1281 | * period elapses, in other words after all currently executing RCU | |
1282 | * read-side critical sections have completed. call_rcu_tasks_rude() | |
1283 | * assumes that the read-side critical sections end at context switch, | |
8af9e2c7 | 1284 | * cond_resched_tasks_rcu_qs(), or transition to usermode execution (as |
a6517e9c NU |
1285 | * usermode execution is schedulable). As such, there are no read-side |
1286 | * primitives analogous to rcu_read_lock() and rcu_read_unlock() because | |
1287 | * this primitive is intended to determine that all tasks have passed | |
1288 | * through a safe state, not so much for data-structure synchronization. | |
c84aad76 PM |
1289 | * |
1290 | * See the description of call_rcu() for more detailed information on | |
1291 | * memory ordering guarantees. | |
1292 | */ | |
1293 | void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func) | |
1294 | { | |
1295 | call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude); | |
1296 | } | |
1297 | EXPORT_SYMBOL_GPL(call_rcu_tasks_rude); | |
1298 | ||
1299 | /** | |
1300 | * synchronize_rcu_tasks_rude - wait for a rude rcu-tasks grace period | |
1301 | * | |
1302 | * Control will return to the caller some time after a rude rcu-tasks | |
1303 | * grace period has elapsed, in other words after all currently | |
1304 | * executing rcu-tasks read-side critical sections have elapsed. These | |
1305 | * read-side critical sections are delimited by calls to schedule(), | |
a6517e9c NU |
1306 | * cond_resched_tasks_rcu_qs(), userspace execution (which is a schedulable |
1307 | * context), and (in theory, anyway) cond_resched(). | |
c84aad76 PM |
1308 | * |
1309 | * This is a very specialized primitive, intended only for a few uses in | |
1310 | * tracing and other situations requiring manipulation of function preambles | |
1311 | * and profiling hooks. The synchronize_rcu_tasks_rude() function is not | |
1312 | * (yet) intended for heavy use from multiple CPUs. | |
1313 | * | |
1314 | * See the description of synchronize_rcu() for more detailed information | |
1315 | * on memory ordering guarantees. | |
1316 | */ | |
1317 | void synchronize_rcu_tasks_rude(void) | |
1318 | { | |
1319 | synchronize_rcu_tasks_generic(&rcu_tasks_rude); | |
1320 | } | |
1321 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude); | |
1322 | ||
1323 | /** | |
1324 | * rcu_barrier_tasks_rude - Wait for in-flight call_rcu_tasks_rude() callbacks. | |
1325 | * | |
1326 | * Although the current implementation is guaranteed to wait, it is not | |
1327 | * obligated to, for example, if there are no pending callbacks. | |
1328 | */ | |
1329 | void rcu_barrier_tasks_rude(void) | |
1330 | { | |
ce9b1c66 | 1331 | rcu_barrier_tasks_generic(&rcu_tasks_rude); |
c84aad76 PM |
1332 | } |
1333 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); | |
1334 | ||
450d461a PM |
1335 | int rcu_tasks_rude_lazy_ms = -1; |
1336 | module_param(rcu_tasks_rude_lazy_ms, int, 0444); | |
1337 | ||
c84aad76 PM |
1338 | static int __init rcu_spawn_tasks_rude_kthread(void) |
1339 | { | |
4fe192df | 1340 | rcu_tasks_rude.gp_sleep = HZ / 10; |
450d461a PM |
1341 | if (rcu_tasks_rude_lazy_ms >= 0) |
1342 | rcu_tasks_rude.lazy_jiffies = msecs_to_jiffies(rcu_tasks_rude_lazy_ms); | |
c84aad76 PM |
1343 | rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude); |
1344 | return 0; | |
1345 | } | |
c84aad76 | 1346 | |
27c0f144 PM |
1347 | #if !defined(CONFIG_TINY_RCU) |
1348 | void show_rcu_tasks_rude_gp_kthread(void) | |
e21408ce PM |
1349 | { |
1350 | show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, ""); | |
1351 | } | |
27c0f144 PM |
1352 | EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread); |
1353 | #endif // !defined(CONFIG_TINY_RCU) | |
a15ec57c PM |
1354 | |
1355 | struct task_struct *get_rcu_tasks_rude_gp_kthread(void) | |
1356 | { | |
1357 | return rcu_tasks_rude.kthread_ptr; | |
1358 | } | |
1359 | EXPORT_SYMBOL_GPL(get_rcu_tasks_rude_gp_kthread); | |
1360 | ||
27c0f144 | 1361 | #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ |
d5f177d3 PM |
1362 | |
1363 | //////////////////////////////////////////////////////////////////////// | |
1364 | // | |
1365 | // Tracing variant of Tasks RCU. This variant is designed to be used | |
1366 | // to protect tracing hooks, including those of BPF. This variant | |
1367 | // therefore: | |
1368 | // | |
1369 | // 1. Has explicit read-side markers to allow finite grace periods | |
1370 | // in the face of in-kernel loops for PREEMPT=n builds. | |
1371 | // | |
1372 | // 2. Protects code in the idle loop, exception entry/exit, and | |
1373 | // CPU-hotplug code paths, similar to the capabilities of SRCU. | |
1374 | // | |
c4f113ac | 1375 | // 3. Avoids expensive read-side instructions, having overhead similar |
d5f177d3 PM |
1376 | // to that of Preemptible RCU. |
1377 | // | |
eea3423b PM |
1378 | // There are of course downsides. For example, the grace-period code |
1379 | // can send IPIs to CPUs, even when those CPUs are in the idle loop or | |
1380 | // in nohz_full userspace. If needed, these downsides can be at least | |
1381 | // partially remedied. | |
d5f177d3 PM |
1382 | // |
1383 | // Perhaps most important, this variant of RCU does not affect the vanilla | |
1384 | // flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace | |
1385 | // readers can operate from idle, offline, and exception entry/exit in no | |
1386 | // way allows rcu_preempt and rcu_sched readers to also do so. | |
a434dd10 PM |
1387 | // |
1388 | // The implementation uses rcu_tasks_wait_gp(), which relies on function | |
1389 | // pointers in the rcu_tasks structure. The rcu_spawn_tasks_trace_kthread() | |
1390 | // function sets these function pointers up so that rcu_tasks_wait_gp() | |
1391 | // invokes these functions in this order: | |
1392 | // | |
1393 | // rcu_tasks_trace_pregp_step(): | |
eea3423b PM |
1394 | // Disables CPU hotplug, adds all currently executing tasks to the |
1395 | // holdout list, then checks the state of all tasks that blocked | |
1396 | // or were preempted within their current RCU Tasks Trace read-side | |
1397 | // critical section, adding them to the holdout list if appropriate. | |
1398 | // Finally, this function re-enables CPU hotplug. | |
1399 | // The ->pertask_func() pointer is NULL, so there is no per-task processing. | |
a434dd10 | 1400 | // rcu_tasks_trace_postscan(): |
eea3423b PM |
1401 | // Invokes synchronize_rcu() to wait for late-stage exiting tasks |
1402 | // to finish exiting. | |
a434dd10 PM |
1403 | // check_all_holdout_tasks_trace(), repeatedly until holdout list is empty: |
1404 | // Scans the holdout list, attempting to identify a quiescent state | |
1405 | // for each task on the list. If there is a quiescent state, the | |
eea3423b PM |
1406 | // corresponding task is removed from the holdout list. Once this |
1407 | // list is empty, the grace period has completed. | |
a434dd10 | 1408 | // rcu_tasks_trace_postgp(): |
eea3423b | 1409 | // Provides the needed full memory barrier and does debug checks. |
a434dd10 PM |
1410 | // |
1411 | // The exit_tasks_rcu_finish_trace() synchronizes with exiting tasks. | |
1412 | // | |
eea3423b PM |
1413 | // Pre-grace-period update-side code is ordered before the grace period |
1414 | // via the ->cbs_lock and barriers in rcu_tasks_kthread(). Pre-grace-period | |
1415 | // read-side code is ordered before the grace period by atomic operations | |
1416 | // on .b.need_qs flag of each task involved in this process, or by scheduler | |
1417 | // context-switch ordering (for locked-down non-running readers). | |
d5f177d3 PM |
1418 | |
1419 | // The lockdep state must be outside of #ifdef to be useful. | |
1420 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
1421 | static struct lock_class_key rcu_lock_trace_key; | |
1422 | struct lockdep_map rcu_trace_lock_map = | |
1423 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_trace", &rcu_lock_trace_key); | |
1424 | EXPORT_SYMBOL_GPL(rcu_trace_lock_map); | |
1425 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
1426 | ||
1427 | #ifdef CONFIG_TASKS_TRACE_RCU | |
1428 | ||
d5f177d3 PM |
1429 | // Record outstanding IPIs to each CPU. No point in sending two... |
1430 | static DEFINE_PER_CPU(bool, trc_ipi_to_cpu); | |
1431 | ||
40471509 PM |
1432 | // The number of detections of task quiescent state relying on |
1433 | // heavyweight readers executing explicit memory barriers. | |
6731da9e PM |
1434 | static unsigned long n_heavy_reader_attempts; |
1435 | static unsigned long n_heavy_reader_updates; | |
1436 | static unsigned long n_heavy_reader_ofl_updates; | |
ffcc21a3 | 1437 | static unsigned long n_trc_holdouts; |
40471509 | 1438 | |
b0afa0f0 PM |
1439 | void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); |
1440 | DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace, | |
1441 | "RCU Tasks Trace"); | |
1442 | ||
3847b645 PM |
1443 | /* Load from ->trc_reader_special.b.need_qs with proper ordering. */ |
1444 | static u8 rcu_ld_need_qs(struct task_struct *t) | |
1445 | { | |
1446 | smp_mb(); // Enforce full grace-period ordering. | |
1447 | return smp_load_acquire(&t->trc_reader_special.b.need_qs); | |
1448 | } | |
1449 | ||
1450 | /* Store to ->trc_reader_special.b.need_qs with proper ordering. */ | |
1451 | static void rcu_st_need_qs(struct task_struct *t, u8 v) | |
1452 | { | |
1453 | smp_store_release(&t->trc_reader_special.b.need_qs, v); | |
1454 | smp_mb(); // Enforce full grace-period ordering. | |
1455 | } | |
1456 | ||
1457 | /* | |
1458 | * Do a cmpxchg() on ->trc_reader_special.b.need_qs, allowing for | |
1459 | * the four-byte operand-size restriction of some platforms. | |
1460 | * Returns the old value, which is often ignored. | |
1461 | */ | |
1462 | u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new) | |
1463 | { | |
1464 | union rcu_special ret; | |
1465 | union rcu_special trs_old = READ_ONCE(t->trc_reader_special); | |
1466 | union rcu_special trs_new = trs_old; | |
1467 | ||
1468 | if (trs_old.b.need_qs != old) | |
1469 | return trs_old.b.need_qs; | |
1470 | trs_new.b.need_qs = new; | |
1471 | ret.s = cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s); | |
1472 | return ret.b.need_qs; | |
1473 | } | |
1474 | EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs); | |
1475 | ||
eea3423b PM |
1476 | /* |
1477 | * If we are the last reader, signal the grace-period kthread. | |
1478 | * Also remove from the per-CPU list of blocked tasks. | |
1479 | */ | |
a5c071cc | 1480 | void rcu_read_unlock_trace_special(struct task_struct *t) |
d5f177d3 | 1481 | { |
0bcb3868 PM |
1482 | unsigned long flags; |
1483 | struct rcu_tasks_percpu *rtpcp; | |
1484 | union rcu_special trs; | |
1485 | ||
1486 | // Open-coded full-word version of rcu_ld_need_qs(). | |
1487 | smp_mb(); // Enforce full grace-period ordering. | |
1488 | trs = smp_load_acquire(&t->trc_reader_special); | |
276c4104 | 1489 | |
3847b645 | 1490 | if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && t->trc_reader_special.b.need_mb) |
276c4104 PM |
1491 | smp_mb(); // Pairs with update-side barriers. |
1492 | // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers. | |
0bcb3868 | 1493 | if (trs.b.need_qs == (TRC_NEED_QS_CHECKED | TRC_NEED_QS)) { |
3847b645 PM |
1494 | u8 result = rcu_trc_cmpxchg_need_qs(t, TRC_NEED_QS_CHECKED | TRC_NEED_QS, |
1495 | TRC_NEED_QS_CHECKED); | |
1496 | ||
0bcb3868 PM |
1497 | WARN_ONCE(result != trs.b.need_qs, "%s: result = %d", __func__, result); |
1498 | } | |
1499 | if (trs.b.blocked) { | |
1500 | rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, t->trc_blkd_cpu); | |
1501 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
1502 | list_del_init(&t->trc_blkd_node); | |
1503 | WRITE_ONCE(t->trc_reader_special.b.blocked, false); | |
1504 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
3847b645 | 1505 | } |
a5c071cc | 1506 | WRITE_ONCE(t->trc_reader_nesting, 0); |
d5f177d3 PM |
1507 | } |
1508 | EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special); | |
1509 | ||
0356d4e6 PM |
1510 | /* Add a newly blocked reader task to its CPU's list. */ |
1511 | void rcu_tasks_trace_qs_blkd(struct task_struct *t) | |
1512 | { | |
1513 | unsigned long flags; | |
1514 | struct rcu_tasks_percpu *rtpcp; | |
1515 | ||
1516 | local_irq_save(flags); | |
1517 | rtpcp = this_cpu_ptr(rcu_tasks_trace.rtpcpu); | |
1518 | raw_spin_lock_rcu_node(rtpcp); // irqs already disabled | |
1519 | t->trc_blkd_cpu = smp_processor_id(); | |
1520 | if (!rtpcp->rtp_blkd_tasks.next) | |
1521 | INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); | |
1522 | list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks); | |
0bcb3868 | 1523 | WRITE_ONCE(t->trc_reader_special.b.blocked, true); |
0356d4e6 PM |
1524 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); |
1525 | } | |
1526 | EXPORT_SYMBOL_GPL(rcu_tasks_trace_qs_blkd); | |
1527 | ||
d5f177d3 PM |
1528 | /* Add a task to the holdout list, if it is not already on the list. */ |
1529 | static void trc_add_holdout(struct task_struct *t, struct list_head *bhp) | |
1530 | { | |
1531 | if (list_empty(&t->trc_holdout_list)) { | |
1532 | get_task_struct(t); | |
1533 | list_add(&t->trc_holdout_list, bhp); | |
ffcc21a3 | 1534 | n_trc_holdouts++; |
d5f177d3 PM |
1535 | } |
1536 | } | |
1537 | ||
1538 | /* Remove a task from the holdout list, if it is in fact present. */ | |
1539 | static void trc_del_holdout(struct task_struct *t) | |
1540 | { | |
1541 | if (!list_empty(&t->trc_holdout_list)) { | |
1542 | list_del_init(&t->trc_holdout_list); | |
1543 | put_task_struct(t); | |
ffcc21a3 | 1544 | n_trc_holdouts--; |
d5f177d3 PM |
1545 | } |
1546 | } | |
1547 | ||
1548 | /* IPI handler to check task state. */ | |
1549 | static void trc_read_check_handler(void *t_in) | |
1550 | { | |
9ff86b4c | 1551 | int nesting; |
d5f177d3 PM |
1552 | struct task_struct *t = current; |
1553 | struct task_struct *texp = t_in; | |
1554 | ||
1555 | // If the task is no longer running on this CPU, leave. | |
3847b645 | 1556 | if (unlikely(texp != t)) |
d5f177d3 | 1557 | goto reset_ipi; // Already on holdout list, so will check later. |
d5f177d3 PM |
1558 | |
1559 | // If the task is not in a read-side critical section, and | |
1560 | // if this is the last reader, awaken the grace-period kthread. | |
9ff86b4c PM |
1561 | nesting = READ_ONCE(t->trc_reader_nesting); |
1562 | if (likely(!nesting)) { | |
3847b645 | 1563 | rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); |
d5f177d3 PM |
1564 | goto reset_ipi; |
1565 | } | |
ba3a86e4 | 1566 | // If we are racing with an rcu_read_unlock_trace(), try again later. |
9ff86b4c | 1567 | if (unlikely(nesting < 0)) |
ba3a86e4 | 1568 | goto reset_ipi; |
d5f177d3 | 1569 | |
eea3423b PM |
1570 | // Get here if the task is in a read-side critical section. |
1571 | // Set its state so that it will update state for the grace-period | |
1572 | // kthread upon exit from that critical section. | |
55061126 | 1573 | rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED); |
d5f177d3 PM |
1574 | |
1575 | reset_ipi: | |
1576 | // Allow future IPIs to be sent on CPU and for task. | |
1577 | // Also order this IPI handler against any later manipulations of | |
1578 | // the intended task. | |
8211e922 | 1579 | smp_store_release(per_cpu_ptr(&trc_ipi_to_cpu, smp_processor_id()), false); // ^^^ |
d5f177d3 PM |
1580 | smp_store_release(&texp->trc_ipi_to_cpu, -1); // ^^^ |
1581 | } | |
1582 | ||
1583 | /* Callback function for scheduler to check locked-down task. */ | |
3847b645 | 1584 | static int trc_inspect_reader(struct task_struct *t, void *bhp_in) |
d5f177d3 | 1585 | { |
3847b645 | 1586 | struct list_head *bhp = bhp_in; |
7d0c9c50 | 1587 | int cpu = task_cpu(t); |
18f08e75 | 1588 | int nesting; |
7e3b70e0 | 1589 | bool ofl = cpu_is_offline(cpu); |
7d0c9c50 | 1590 | |
897ba84d | 1591 | if (task_curr(t) && !ofl) { |
7d0c9c50 | 1592 | // If no chance of heavyweight readers, do it the hard way. |
897ba84d | 1593 | if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) |
9b3c4ab3 | 1594 | return -EINVAL; |
7d0c9c50 PM |
1595 | |
1596 | // If heavyweight readers are enabled on the remote task, | |
1597 | // we can inspect its state despite its currently running. | |
1598 | // However, we cannot safely change its state. | |
40471509 | 1599 | n_heavy_reader_attempts++; |
897ba84d PM |
1600 | // Check for "running" idle tasks on offline CPUs. |
1601 | if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) | |
9b3c4ab3 | 1602 | return -EINVAL; // No quiescent state, do it the hard way. |
40471509 | 1603 | n_heavy_reader_updates++; |
18f08e75 | 1604 | nesting = 0; |
7d0c9c50 | 1605 | } else { |
bdb0cca0 | 1606 | // The task is not running, so C-language access is safe. |
18f08e75 | 1607 | nesting = t->trc_reader_nesting; |
a80712b9 | 1608 | WARN_ON_ONCE(ofl && task_curr(t) && (t != idle_task(task_cpu(t)))); |
897ba84d PM |
1609 | if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && ofl) |
1610 | n_heavy_reader_ofl_updates++; | |
7d0c9c50 | 1611 | } |
d5f177d3 | 1612 | |
18f08e75 PM |
1613 | // If not exiting a read-side critical section, mark as checked |
1614 | // so that the grace-period kthread will remove it from the | |
1615 | // holdout list. | |
0968e892 PM |
1616 | if (!nesting) { |
1617 | rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); | |
1618 | return 0; // In QS, so done. | |
3847b645 | 1619 | } |
0968e892 | 1620 | if (nesting < 0) |
eea3423b | 1621 | return -EINVAL; // Reader transitioning, try again later. |
7d0c9c50 PM |
1622 | |
1623 | // The task is in a read-side critical section, so set up its | |
0968e892 PM |
1624 | // state so that it will update state upon exit from that critical |
1625 | // section. | |
55061126 | 1626 | if (!rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED)) |
3847b645 | 1627 | trc_add_holdout(t, bhp); |
9b3c4ab3 | 1628 | return 0; |
d5f177d3 PM |
1629 | } |
1630 | ||
1631 | /* Attempt to extract the state for the specified task. */ | |
1632 | static void trc_wait_for_one_reader(struct task_struct *t, | |
1633 | struct list_head *bhp) | |
1634 | { | |
1635 | int cpu; | |
1636 | ||
1637 | // If a previous IPI is still in flight, let it complete. | |
1638 | if (smp_load_acquire(&t->trc_ipi_to_cpu) != -1) // Order IPI | |
1639 | return; | |
1640 | ||
1641 | // The current task had better be in a quiescent state. | |
1642 | if (t == current) { | |
3847b645 | 1643 | rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); |
bdb0cca0 | 1644 | WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); |
d5f177d3 PM |
1645 | return; |
1646 | } | |
1647 | ||
1648 | // Attempt to nail down the task for inspection. | |
1649 | get_task_struct(t); | |
3847b645 | 1650 | if (!task_call_func(t, trc_inspect_reader, bhp)) { |
d5f177d3 PM |
1651 | put_task_struct(t); |
1652 | return; | |
1653 | } | |
1654 | put_task_struct(t); | |
1655 | ||
45f4b4a2 PM |
1656 | // If this task is not yet on the holdout list, then we are in |
1657 | // an RCU read-side critical section. Otherwise, the invocation of | |
d0a85858 | 1658 | // trc_add_holdout() that added it to the list did the necessary |
45f4b4a2 PM |
1659 | // get_task_struct(). Either way, the task cannot be freed out |
1660 | // from under this code. | |
1661 | ||
d5f177d3 PM |
1662 | // If currently running, send an IPI, either way, add to list. |
1663 | trc_add_holdout(t, bhp); | |
574de876 PM |
1664 | if (task_curr(t) && |
1665 | time_after(jiffies + 1, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) { | |
d5f177d3 PM |
1666 | // The task is currently running, so try IPIing it. |
1667 | cpu = task_cpu(t); | |
1668 | ||
1669 | // If there is already an IPI outstanding, let it happen. | |
1670 | if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0) | |
1671 | return; | |
1672 | ||
d5f177d3 PM |
1673 | per_cpu(trc_ipi_to_cpu, cpu) = true; |
1674 | t->trc_ipi_to_cpu = cpu; | |
238dbce3 | 1675 | rcu_tasks_trace.n_ipis++; |
96017bf9 | 1676 | if (smp_call_function_single(cpu, trc_read_check_handler, t, 0)) { |
d5f177d3 PM |
1677 | // Just in case there is some other reason for |
1678 | // failure than the target CPU being offline. | |
46aa886c NU |
1679 | WARN_ONCE(1, "%s(): smp_call_function_single() failed for CPU: %d\n", |
1680 | __func__, cpu); | |
7e0669c3 | 1681 | rcu_tasks_trace.n_ipis_fails++; |
d5f177d3 | 1682 | per_cpu(trc_ipi_to_cpu, cpu) = false; |
46aa886c | 1683 | t->trc_ipi_to_cpu = -1; |
d5f177d3 PM |
1684 | } |
1685 | } | |
1686 | } | |
1687 | ||
7460ade1 PM |
1688 | /* |
1689 | * Initialize for first-round processing for the specified task. | |
1690 | * Return false if task is NULL or already taken care of, true otherwise. | |
1691 | */ | |
1692 | static bool rcu_tasks_trace_pertask_prep(struct task_struct *t, bool notself) | |
d5f177d3 | 1693 | { |
1b04fa99 | 1694 | // During early boot when there is only the one boot CPU, there |
19415004 PM |
1695 | // is no idle task for the other CPUs. Also, the grace-period |
1696 | // kthread is always in a quiescent state. In addition, just return | |
1697 | // if this task is already on the list. | |
7460ade1 PM |
1698 | if (unlikely(t == NULL) || (t == current && notself) || !list_empty(&t->trc_holdout_list)) |
1699 | return false; | |
1b04fa99 | 1700 | |
3847b645 | 1701 | rcu_st_need_qs(t, 0); |
d5f177d3 | 1702 | t->trc_ipi_to_cpu = -1; |
7460ade1 PM |
1703 | return true; |
1704 | } | |
1705 | ||
1706 | /* Do first-round processing for the specified task. */ | |
1707 | static void rcu_tasks_trace_pertask(struct task_struct *t, struct list_head *hop) | |
1708 | { | |
1709 | if (rcu_tasks_trace_pertask_prep(t, true)) | |
1710 | trc_wait_for_one_reader(t, hop); | |
1711 | } | |
1712 | ||
1fa98e2e | 1713 | /* Initialize for a new RCU-tasks-trace grace period. */ |
7460ade1 | 1714 | static void rcu_tasks_trace_pregp_step(struct list_head *hop) |
1fa98e2e | 1715 | { |
dc7d54b4 | 1716 | LIST_HEAD(blkd_tasks); |
1fa98e2e | 1717 | int cpu; |
dc7d54b4 PM |
1718 | unsigned long flags; |
1719 | struct rcu_tasks_percpu *rtpcp; | |
1720 | struct task_struct *t; | |
1fa98e2e PM |
1721 | |
1722 | // There shouldn't be any old IPIs, but... | |
1723 | for_each_possible_cpu(cpu) | |
1724 | WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu)); | |
1725 | ||
eea3423b PM |
1726 | // Disable CPU hotplug across the CPU scan for the benefit of |
1727 | // any IPIs that might be needed. This also waits for all readers | |
1728 | // in CPU-hotplug code paths. | |
1fa98e2e | 1729 | cpus_read_lock(); |
7460ade1 | 1730 | |
eea3423b | 1731 | // These rcu_tasks_trace_pertask_prep() calls are serialized to |
7460ade1 | 1732 | // allow safe access to the hop list. |
e386b672 PM |
1733 | for_each_online_cpu(cpu) { |
1734 | rcu_read_lock(); | |
1735 | t = cpu_curr_snapshot(cpu); | |
1736 | if (rcu_tasks_trace_pertask_prep(t, true)) | |
1737 | trc_add_holdout(t, hop); | |
1738 | rcu_read_unlock(); | |
d6ad6063 | 1739 | cond_resched_tasks_rcu_qs(); |
e386b672 | 1740 | } |
dc7d54b4 PM |
1741 | |
1742 | // Only after all running tasks have been accounted for is it | |
1743 | // safe to take care of the tasks that have blocked within their | |
1744 | // current RCU tasks trace read-side critical section. | |
1745 | for_each_possible_cpu(cpu) { | |
1746 | rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, cpu); | |
1747 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
1748 | list_splice_init(&rtpcp->rtp_blkd_tasks, &blkd_tasks); | |
1749 | while (!list_empty(&blkd_tasks)) { | |
1750 | rcu_read_lock(); | |
1751 | t = list_first_entry(&blkd_tasks, struct task_struct, trc_blkd_node); | |
1752 | list_del_init(&t->trc_blkd_node); | |
1753 | list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks); | |
1754 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
1755 | rcu_tasks_trace_pertask(t, hop); | |
1756 | rcu_read_unlock(); | |
1757 | raw_spin_lock_irqsave_rcu_node(rtpcp, flags); | |
1758 | } | |
1759 | raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); | |
d6ad6063 | 1760 | cond_resched_tasks_rcu_qs(); |
dc7d54b4 | 1761 | } |
56096ecd PM |
1762 | |
1763 | // Re-enable CPU hotplug now that the holdout list is populated. | |
1764 | cpus_read_unlock(); | |
1fa98e2e PM |
1765 | } |
1766 | ||
9796e1ae | 1767 | /* |
955a0192 | 1768 | * Do intermediate processing between task and holdout scans. |
9796e1ae PM |
1769 | */ |
1770 | static void rcu_tasks_trace_postscan(struct list_head *hop) | |
d5f177d3 PM |
1771 | { |
1772 | // Wait for late-stage exiting tasks to finish exiting. | |
1773 | // These might have passed the call to exit_tasks_rcu_finish(). | |
e6c86c51 PM |
1774 | |
1775 | // If you remove the following line, update rcu_trace_implies_rcu_gp()!!! | |
d5f177d3 | 1776 | synchronize_rcu(); |
3847b645 PM |
1777 | // Any tasks that exit after this point will set |
1778 | // TRC_NEED_QS_CHECKED in ->trc_reader_special.b.need_qs. | |
d5f177d3 PM |
1779 | } |
1780 | ||
65b629e7 NU |
1781 | /* Communicate task state back to the RCU tasks trace stall warning request. */ |
1782 | struct trc_stall_chk_rdr { | |
1783 | int nesting; | |
1784 | int ipi_to_cpu; | |
1785 | u8 needqs; | |
1786 | }; | |
1787 | ||
1788 | static int trc_check_slow_task(struct task_struct *t, void *arg) | |
1789 | { | |
1790 | struct trc_stall_chk_rdr *trc_rdrp = arg; | |
1791 | ||
f90f19da | 1792 | if (task_curr(t) && cpu_online(task_cpu(t))) |
65b629e7 NU |
1793 | return false; // It is running, so decline to inspect it. |
1794 | trc_rdrp->nesting = READ_ONCE(t->trc_reader_nesting); | |
1795 | trc_rdrp->ipi_to_cpu = READ_ONCE(t->trc_ipi_to_cpu); | |
3847b645 | 1796 | trc_rdrp->needqs = rcu_ld_need_qs(t); |
65b629e7 NU |
1797 | return true; |
1798 | } | |
1799 | ||
4593e772 PM |
1800 | /* Show the state of a task stalling the current RCU tasks trace GP. */ |
1801 | static void show_stalled_task_trace(struct task_struct *t, bool *firstreport) | |
1802 | { | |
1803 | int cpu; | |
65b629e7 NU |
1804 | struct trc_stall_chk_rdr trc_rdr; |
1805 | bool is_idle_tsk = is_idle_task(t); | |
4593e772 PM |
1806 | |
1807 | if (*firstreport) { | |
1808 | pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n"); | |
1809 | *firstreport = false; | |
1810 | } | |
4593e772 | 1811 | cpu = task_cpu(t); |
65b629e7 | 1812 | if (!task_call_func(t, trc_check_slow_task, &trc_rdr)) |
9f3eb5fb | 1813 | pr_alert("P%d: %c%c\n", |
65b629e7 | 1814 | t->pid, |
9f3eb5fb | 1815 | ".I"[t->trc_ipi_to_cpu >= 0], |
65b629e7 NU |
1816 | ".i"[is_idle_tsk]); |
1817 | else | |
387c0ad7 | 1818 | pr_alert("P%d: %c%c%c%c nesting: %d%c%c cpu: %d%s\n", |
65b629e7 NU |
1819 | t->pid, |
1820 | ".I"[trc_rdr.ipi_to_cpu >= 0], | |
1821 | ".i"[is_idle_tsk], | |
1822 | ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)], | |
387c0ad7 | 1823 | ".B"[!!data_race(t->trc_reader_special.b.blocked)], |
65b629e7 | 1824 | trc_rdr.nesting, |
be15a164 PM |
1825 | " !CN"[trc_rdr.needqs & 0x3], |
1826 | " ?"[trc_rdr.needqs > 0x3], | |
c8c03ad9 | 1827 | cpu, cpu_online(cpu) ? "" : "(offline)"); |
4593e772 PM |
1828 | sched_show_task(t); |
1829 | } | |
1830 | ||
1831 | /* List stalled IPIs for RCU tasks trace. */ | |
1832 | static void show_stalled_ipi_trace(void) | |
1833 | { | |
1834 | int cpu; | |
1835 | ||
1836 | for_each_possible_cpu(cpu) | |
1837 | if (per_cpu(trc_ipi_to_cpu, cpu)) | |
1838 | pr_alert("\tIPI outstanding to CPU %d\n", cpu); | |
1839 | } | |
1840 | ||
d5f177d3 PM |
1841 | /* Do one scan of the holdout list. */ |
1842 | static void check_all_holdout_tasks_trace(struct list_head *hop, | |
4593e772 | 1843 | bool needreport, bool *firstreport) |
d5f177d3 PM |
1844 | { |
1845 | struct task_struct *g, *t; | |
1846 | ||
eea3423b | 1847 | // Disable CPU hotplug across the holdout list scan for IPIs. |
81b4a7bc PM |
1848 | cpus_read_lock(); |
1849 | ||
d5f177d3 PM |
1850 | list_for_each_entry_safe(t, g, hop, trc_holdout_list) { |
1851 | // If safe and needed, try to check the current task. | |
1852 | if (READ_ONCE(t->trc_ipi_to_cpu) == -1 && | |
3847b645 | 1853 | !(rcu_ld_need_qs(t) & TRC_NEED_QS_CHECKED)) |
d5f177d3 PM |
1854 | trc_wait_for_one_reader(t, hop); |
1855 | ||
1856 | // If check succeeded, remove this task from the list. | |
f5dbc594 | 1857 | if (smp_load_acquire(&t->trc_ipi_to_cpu) == -1 && |
3847b645 | 1858 | rcu_ld_need_qs(t) == TRC_NEED_QS_CHECKED) |
d5f177d3 | 1859 | trc_del_holdout(t); |
4593e772 PM |
1860 | else if (needreport) |
1861 | show_stalled_task_trace(t, firstreport); | |
d6ad6063 | 1862 | cond_resched_tasks_rcu_qs(); |
4593e772 | 1863 | } |
81b4a7bc PM |
1864 | |
1865 | // Re-enable CPU hotplug now that the holdout list scan has completed. | |
1866 | cpus_read_unlock(); | |
1867 | ||
4593e772 | 1868 | if (needreport) { |
89401176 | 1869 | if (*firstreport) |
4593e772 PM |
1870 | pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n"); |
1871 | show_stalled_ipi_trace(); | |
d5f177d3 PM |
1872 | } |
1873 | } | |
1874 | ||
cbe0d8d9 PM |
1875 | static void rcu_tasks_trace_empty_fn(void *unused) |
1876 | { | |
1877 | } | |
1878 | ||
d5f177d3 | 1879 | /* Wait for grace period to complete and provide ordering. */ |
af051ca4 | 1880 | static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) |
d5f177d3 | 1881 | { |
cbe0d8d9 | 1882 | int cpu; |
4593e772 | 1883 | |
cbe0d8d9 PM |
1884 | // Wait for any lingering IPI handlers to complete. Note that |
1885 | // if a CPU has gone offline or transitioned to userspace in the | |
1886 | // meantime, all IPI handlers should have been drained beforehand. | |
1887 | // Yes, this assumes that CPUs process IPIs in order. If that ever | |
1888 | // changes, there will need to be a recheck and/or timed wait. | |
1889 | for_each_online_cpu(cpu) | |
f5dbc594 | 1890 | if (WARN_ON_ONCE(smp_load_acquire(per_cpu_ptr(&trc_ipi_to_cpu, cpu)))) |
cbe0d8d9 PM |
1891 | smp_call_function_single(cpu, rcu_tasks_trace_empty_fn, NULL, 1); |
1892 | ||
d5f177d3 | 1893 | smp_mb(); // Caller's code must be ordered after wakeup. |
43766c3e | 1894 | // Pairs with pretty much every ordering primitive. |
d5f177d3 PM |
1895 | } |
1896 | ||
1897 | /* Report any needed quiescent state for this exiting task. */ | |
25246fc8 | 1898 | static void exit_tasks_rcu_finish_trace(struct task_struct *t) |
d5f177d3 | 1899 | { |
0356d4e6 PM |
1900 | union rcu_special trs = READ_ONCE(t->trc_reader_special); |
1901 | ||
3847b645 | 1902 | rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); |
bdb0cca0 | 1903 | WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); |
0bcb3868 | 1904 | if (WARN_ON_ONCE(rcu_ld_need_qs(t) & TRC_NEED_QS || trs.b.blocked)) |
a5c071cc | 1905 | rcu_read_unlock_trace_special(t); |
3847b645 PM |
1906 | else |
1907 | WRITE_ONCE(t->trc_reader_nesting, 0); | |
d5f177d3 PM |
1908 | } |
1909 | ||
d5f177d3 PM |
1910 | /** |
1911 | * call_rcu_tasks_trace() - Queue a callback trace task-based grace period | |
1912 | * @rhp: structure to be used for queueing the RCU updates. | |
1913 | * @func: actual callback function to be invoked after the grace period | |
1914 | * | |
ed42c380 NU |
1915 | * The callback function will be invoked some time after a trace rcu-tasks |
1916 | * grace period elapses, in other words after all currently executing | |
1917 | * trace rcu-tasks read-side critical sections have completed. These | |
1918 | * read-side critical sections are delimited by calls to rcu_read_lock_trace() | |
1919 | * and rcu_read_unlock_trace(). | |
d5f177d3 PM |
1920 | * |
1921 | * See the description of call_rcu() for more detailed information on | |
1922 | * memory ordering guarantees. | |
1923 | */ | |
1924 | void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func) | |
1925 | { | |
1926 | call_rcu_tasks_generic(rhp, func, &rcu_tasks_trace); | |
1927 | } | |
1928 | EXPORT_SYMBOL_GPL(call_rcu_tasks_trace); | |
1929 | ||
1930 | /** | |
1931 | * synchronize_rcu_tasks_trace - wait for a trace rcu-tasks grace period | |
1932 | * | |
1933 | * Control will return to the caller some time after a trace rcu-tasks | |
c7dcf810 | 1934 | * grace period has elapsed, in other words after all currently executing |
ed42c380 | 1935 | * trace rcu-tasks read-side critical sections have elapsed. These read-side |
c7dcf810 PM |
1936 | * critical sections are delimited by calls to rcu_read_lock_trace() |
1937 | * and rcu_read_unlock_trace(). | |
d5f177d3 PM |
1938 | * |
1939 | * This is a very specialized primitive, intended only for a few uses in | |
1940 | * tracing and other situations requiring manipulation of function preambles | |
1941 | * and profiling hooks. The synchronize_rcu_tasks_trace() function is not | |
1942 | * (yet) intended for heavy use from multiple CPUs. | |
1943 | * | |
1944 | * See the description of synchronize_rcu() for more detailed information | |
1945 | * on memory ordering guarantees. | |
1946 | */ | |
1947 | void synchronize_rcu_tasks_trace(void) | |
1948 | { | |
1949 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_trace_lock_map), "Illegal synchronize_rcu_tasks_trace() in RCU Tasks Trace read-side critical section"); | |
1950 | synchronize_rcu_tasks_generic(&rcu_tasks_trace); | |
1951 | } | |
1952 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace); | |
1953 | ||
1954 | /** | |
1955 | * rcu_barrier_tasks_trace - Wait for in-flight call_rcu_tasks_trace() callbacks. | |
1956 | * | |
1957 | * Although the current implementation is guaranteed to wait, it is not | |
1958 | * obligated to, for example, if there are no pending callbacks. | |
1959 | */ | |
1960 | void rcu_barrier_tasks_trace(void) | |
1961 | { | |
ce9b1c66 | 1962 | rcu_barrier_tasks_generic(&rcu_tasks_trace); |
d5f177d3 PM |
1963 | } |
1964 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); | |
1965 | ||
450d461a PM |
1966 | int rcu_tasks_trace_lazy_ms = -1; |
1967 | module_param(rcu_tasks_trace_lazy_ms, int, 0444); | |
1968 | ||
d5f177d3 PM |
1969 | static int __init rcu_spawn_tasks_trace_kthread(void) |
1970 | { | |
2393a613 | 1971 | if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) { |
4fe192df | 1972 | rcu_tasks_trace.gp_sleep = HZ / 10; |
75dc2da5 | 1973 | rcu_tasks_trace.init_fract = HZ / 10; |
2393a613 | 1974 | } else { |
4fe192df PM |
1975 | rcu_tasks_trace.gp_sleep = HZ / 200; |
1976 | if (rcu_tasks_trace.gp_sleep <= 0) | |
1977 | rcu_tasks_trace.gp_sleep = 1; | |
75dc2da5 | 1978 | rcu_tasks_trace.init_fract = HZ / 200; |
2393a613 PM |
1979 | if (rcu_tasks_trace.init_fract <= 0) |
1980 | rcu_tasks_trace.init_fract = 1; | |
1981 | } | |
450d461a PM |
1982 | if (rcu_tasks_trace_lazy_ms >= 0) |
1983 | rcu_tasks_trace.lazy_jiffies = msecs_to_jiffies(rcu_tasks_trace_lazy_ms); | |
d5f177d3 | 1984 | rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step; |
d5f177d3 PM |
1985 | rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan; |
1986 | rcu_tasks_trace.holdouts_func = check_all_holdout_tasks_trace; | |
1987 | rcu_tasks_trace.postgp_func = rcu_tasks_trace_postgp; | |
1988 | rcu_spawn_tasks_kthread_generic(&rcu_tasks_trace); | |
1989 | return 0; | |
1990 | } | |
d5f177d3 | 1991 | |
27c0f144 PM |
1992 | #if !defined(CONFIG_TINY_RCU) |
1993 | void show_rcu_tasks_trace_gp_kthread(void) | |
e21408ce | 1994 | { |
40471509 | 1995 | char buf[64]; |
e21408ce | 1996 | |
ffcc21a3 PM |
1997 | sprintf(buf, "N%lu h:%lu/%lu/%lu", |
1998 | data_race(n_trc_holdouts), | |
edf3775f | 1999 | data_race(n_heavy_reader_ofl_updates), |
40471509 PM |
2000 | data_race(n_heavy_reader_updates), |
2001 | data_race(n_heavy_reader_attempts)); | |
e21408ce PM |
2002 | show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf); |
2003 | } | |
27c0f144 PM |
2004 | EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread); |
2005 | #endif // !defined(CONFIG_TINY_RCU) | |
e21408ce | 2006 | |
5f8e3202 PM |
2007 | struct task_struct *get_rcu_tasks_trace_gp_kthread(void) |
2008 | { | |
2009 | return rcu_tasks_trace.kthread_ptr; | |
2010 | } | |
2011 | EXPORT_SYMBOL_GPL(get_rcu_tasks_trace_gp_kthread); | |
2012 | ||
d5f177d3 | 2013 | #else /* #ifdef CONFIG_TASKS_TRACE_RCU */ |
25246fc8 | 2014 | static void exit_tasks_rcu_finish_trace(struct task_struct *t) { } |
d5f177d3 | 2015 | #endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */ |
8fd8ca38 | 2016 | |
8344496e | 2017 | #ifndef CONFIG_TINY_RCU |
e21408ce PM |
2018 | void show_rcu_tasks_gp_kthreads(void) |
2019 | { | |
2020 | show_rcu_tasks_classic_gp_kthread(); | |
2021 | show_rcu_tasks_rude_gp_kthread(); | |
2022 | show_rcu_tasks_trace_gp_kthread(); | |
2023 | } | |
8344496e | 2024 | #endif /* #ifndef CONFIG_TINY_RCU */ |
e21408ce | 2025 | |
bfba7ed0 URS |
2026 | #ifdef CONFIG_PROVE_RCU |
2027 | struct rcu_tasks_test_desc { | |
2028 | struct rcu_head rh; | |
2029 | const char *name; | |
2030 | bool notrun; | |
1cf1144e | 2031 | unsigned long runstart; |
bfba7ed0 URS |
2032 | }; |
2033 | ||
2034 | static struct rcu_tasks_test_desc tests[] = { | |
2035 | { | |
2036 | .name = "call_rcu_tasks()", | |
2037 | /* If not defined, the test is skipped. */ | |
1cf1144e | 2038 | .notrun = IS_ENABLED(CONFIG_TASKS_RCU), |
bfba7ed0 URS |
2039 | }, |
2040 | { | |
2041 | .name = "call_rcu_tasks_rude()", | |
2042 | /* If not defined, the test is skipped. */ | |
1cf1144e | 2043 | .notrun = IS_ENABLED(CONFIG_TASKS_RUDE_RCU), |
bfba7ed0 URS |
2044 | }, |
2045 | { | |
2046 | .name = "call_rcu_tasks_trace()", | |
2047 | /* If not defined, the test is skipped. */ | |
1cf1144e | 2048 | .notrun = IS_ENABLED(CONFIG_TASKS_TRACE_RCU) |
bfba7ed0 URS |
2049 | } |
2050 | }; | |
2051 | ||
2052 | static void test_rcu_tasks_callback(struct rcu_head *rhp) | |
2053 | { | |
2054 | struct rcu_tasks_test_desc *rttd = | |
2055 | container_of(rhp, struct rcu_tasks_test_desc, rh); | |
2056 | ||
2057 | pr_info("Callback from %s invoked.\n", rttd->name); | |
2058 | ||
1cf1144e | 2059 | rttd->notrun = false; |
bfba7ed0 URS |
2060 | } |
2061 | ||
2062 | static void rcu_tasks_initiate_self_tests(void) | |
2063 | { | |
bfba7ed0 | 2064 | #ifdef CONFIG_TASKS_RCU |
92a708dc | 2065 | pr_info("Running RCU Tasks wait API self tests\n"); |
9420fb93 | 2066 | tests[0].runstart = jiffies; |
bfba7ed0 URS |
2067 | synchronize_rcu_tasks(); |
2068 | call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback); | |
2069 | #endif | |
2070 | ||
2071 | #ifdef CONFIG_TASKS_RUDE_RCU | |
92a708dc | 2072 | pr_info("Running RCU Tasks Rude wait API self tests\n"); |
9420fb93 | 2073 | tests[1].runstart = jiffies; |
bfba7ed0 URS |
2074 | synchronize_rcu_tasks_rude(); |
2075 | call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback); | |
2076 | #endif | |
2077 | ||
2078 | #ifdef CONFIG_TASKS_TRACE_RCU | |
92a708dc | 2079 | pr_info("Running RCU Tasks Trace wait API self tests\n"); |
9420fb93 | 2080 | tests[2].runstart = jiffies; |
bfba7ed0 URS |
2081 | synchronize_rcu_tasks_trace(); |
2082 | call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback); | |
2083 | #endif | |
2084 | } | |
2085 | ||
e72ee5e1 WL |
2086 | /* |
2087 | * Return: 0 - test passed | |
2088 | * 1 - test failed, but have not timed out yet | |
2089 | * -1 - test failed and timed out | |
2090 | */ | |
bfba7ed0 URS |
2091 | static int rcu_tasks_verify_self_tests(void) |
2092 | { | |
2093 | int ret = 0; | |
2094 | int i; | |
1cf1144e | 2095 | unsigned long bst = rcu_task_stall_timeout; |
bfba7ed0 | 2096 | |
1cf1144e PM |
2097 | if (bst <= 0 || bst > RCU_TASK_BOOT_STALL_TIMEOUT) |
2098 | bst = RCU_TASK_BOOT_STALL_TIMEOUT; | |
bfba7ed0 | 2099 | for (i = 0; i < ARRAY_SIZE(tests); i++) { |
1cf1144e PM |
2100 | while (tests[i].notrun) { // still hanging. |
2101 | if (time_after(jiffies, tests[i].runstart + bst)) { | |
2102 | pr_err("%s has failed boot-time tests.\n", tests[i].name); | |
2103 | ret = -1; | |
2104 | break; | |
2105 | } | |
e72ee5e1 WL |
2106 | ret = 1; |
2107 | break; | |
bfba7ed0 URS |
2108 | } |
2109 | } | |
e72ee5e1 | 2110 | WARN_ON(ret < 0); |
bfba7ed0 URS |
2111 | |
2112 | return ret; | |
2113 | } | |
e72ee5e1 WL |
2114 | |
2115 | /* | |
2116 | * Repeat the rcu_tasks_verify_self_tests() call once every second until the | |
2117 | * test passes or has timed out. | |
2118 | */ | |
2119 | static struct delayed_work rcu_tasks_verify_work; | |
2120 | static void rcu_tasks_verify_work_fn(struct work_struct *work __maybe_unused) | |
2121 | { | |
2122 | int ret = rcu_tasks_verify_self_tests(); | |
2123 | ||
2124 | if (ret <= 0) | |
2125 | return; | |
2126 | ||
2127 | /* Test fails but not timed out yet, reschedule another check */ | |
2128 | schedule_delayed_work(&rcu_tasks_verify_work, HZ); | |
2129 | } | |
2130 | ||
2131 | static int rcu_tasks_verify_schedule_work(void) | |
2132 | { | |
2133 | INIT_DELAYED_WORK(&rcu_tasks_verify_work, rcu_tasks_verify_work_fn); | |
2134 | rcu_tasks_verify_work_fn(NULL); | |
2135 | return 0; | |
2136 | } | |
2137 | late_initcall(rcu_tasks_verify_schedule_work); | |
bfba7ed0 URS |
2138 | #else /* #ifdef CONFIG_PROVE_RCU */ |
2139 | static void rcu_tasks_initiate_self_tests(void) { } | |
2140 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
2141 | ||
30ef0963 PM |
2142 | void __init tasks_cblist_init_generic(void) |
2143 | { | |
2144 | lockdep_assert_irqs_disabled(); | |
2145 | WARN_ON(num_online_cpus() > 1); | |
2146 | ||
2147 | #ifdef CONFIG_TASKS_RCU | |
2148 | cblist_init_generic(&rcu_tasks); | |
2149 | #endif | |
2150 | ||
2151 | #ifdef CONFIG_TASKS_RUDE_RCU | |
2152 | cblist_init_generic(&rcu_tasks_rude); | |
2153 | #endif | |
2154 | ||
2155 | #ifdef CONFIG_TASKS_TRACE_RCU | |
2156 | cblist_init_generic(&rcu_tasks_trace); | |
2157 | #endif | |
2158 | } | |
2159 | ||
1b04fa99 URS |
2160 | void __init rcu_init_tasks_generic(void) |
2161 | { | |
2162 | #ifdef CONFIG_TASKS_RCU | |
2163 | rcu_spawn_tasks_kthread(); | |
2164 | #endif | |
2165 | ||
2166 | #ifdef CONFIG_TASKS_RUDE_RCU | |
2167 | rcu_spawn_tasks_rude_kthread(); | |
2168 | #endif | |
2169 | ||
2170 | #ifdef CONFIG_TASKS_TRACE_RCU | |
2171 | rcu_spawn_tasks_trace_kthread(); | |
2172 | #endif | |
bfba7ed0 URS |
2173 | |
2174 | // Run the self-tests. | |
2175 | rcu_tasks_initiate_self_tests(); | |
1b04fa99 URS |
2176 | } |
2177 | ||
8fd8ca38 PM |
2178 | #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ |
2179 | static inline void rcu_tasks_bootup_oddness(void) {} | |
2180 | #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ |