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