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9549332d DH |
1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* FS-Cache cache handling | |
3 | * | |
4 | * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved. | |
5 | * Written by David Howells (dhowells@redhat.com) | |
6 | */ | |
7 | ||
8 | #define FSCACHE_DEBUG_LEVEL CACHE | |
9 | #include <linux/export.h> | |
10 | #include <linux/slab.h> | |
11 | #include "internal.h" | |
12 | ||
13 | static LIST_HEAD(fscache_caches); | |
14 | DECLARE_RWSEM(fscache_addremove_sem); | |
15 | EXPORT_SYMBOL(fscache_addremove_sem); | |
cdf262f2 DH |
16 | DECLARE_WAIT_QUEUE_HEAD(fscache_clearance_waiters); |
17 | EXPORT_SYMBOL(fscache_clearance_waiters); | |
9549332d DH |
18 | |
19 | static atomic_t fscache_cache_debug_id; | |
20 | ||
21 | /* | |
22 | * Allocate a cache cookie. | |
23 | */ | |
24 | static struct fscache_cache *fscache_alloc_cache(const char *name) | |
25 | { | |
26 | struct fscache_cache *cache; | |
27 | ||
28 | cache = kzalloc(sizeof(*cache), GFP_KERNEL); | |
29 | if (cache) { | |
30 | if (name) { | |
31 | cache->name = kstrdup(name, GFP_KERNEL); | |
32 | if (!cache->name) { | |
33 | kfree(cache); | |
34 | return NULL; | |
35 | } | |
36 | } | |
37 | refcount_set(&cache->ref, 1); | |
38 | INIT_LIST_HEAD(&cache->cache_link); | |
39 | cache->debug_id = atomic_inc_return(&fscache_cache_debug_id); | |
40 | } | |
41 | return cache; | |
42 | } | |
43 | ||
44 | static bool fscache_get_cache_maybe(struct fscache_cache *cache, | |
45 | enum fscache_cache_trace where) | |
46 | { | |
47 | bool success; | |
48 | int ref; | |
49 | ||
50 | success = __refcount_inc_not_zero(&cache->ref, &ref); | |
51 | if (success) | |
52 | trace_fscache_cache(cache->debug_id, ref + 1, where); | |
53 | return success; | |
54 | } | |
55 | ||
56 | /* | |
57 | * Look up a cache cookie. | |
58 | */ | |
59 | struct fscache_cache *fscache_lookup_cache(const char *name, bool is_cache) | |
60 | { | |
61 | struct fscache_cache *candidate, *cache, *unnamed = NULL; | |
62 | ||
63 | /* firstly check for the existence of the cache under read lock */ | |
64 | down_read(&fscache_addremove_sem); | |
65 | ||
66 | list_for_each_entry(cache, &fscache_caches, cache_link) { | |
67 | if (cache->name && name && strcmp(cache->name, name) == 0 && | |
68 | fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) | |
69 | goto got_cache_r; | |
70 | if (!cache->name && !name && | |
71 | fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) | |
72 | goto got_cache_r; | |
73 | } | |
74 | ||
75 | if (!name) { | |
76 | list_for_each_entry(cache, &fscache_caches, cache_link) { | |
77 | if (cache->name && | |
78 | fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) | |
79 | goto got_cache_r; | |
80 | } | |
81 | } | |
82 | ||
83 | up_read(&fscache_addremove_sem); | |
84 | ||
85 | /* the cache does not exist - create a candidate */ | |
86 | candidate = fscache_alloc_cache(name); | |
87 | if (!candidate) | |
88 | return ERR_PTR(-ENOMEM); | |
89 | ||
90 | /* write lock, search again and add if still not present */ | |
91 | down_write(&fscache_addremove_sem); | |
92 | ||
93 | list_for_each_entry(cache, &fscache_caches, cache_link) { | |
94 | if (cache->name && name && strcmp(cache->name, name) == 0 && | |
95 | fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) | |
96 | goto got_cache_w; | |
97 | if (!cache->name) { | |
98 | unnamed = cache; | |
99 | if (!name && | |
100 | fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) | |
101 | goto got_cache_w; | |
102 | } | |
103 | } | |
104 | ||
105 | if (unnamed && is_cache && | |
106 | fscache_get_cache_maybe(unnamed, fscache_cache_get_acquire)) | |
107 | goto use_unnamed_cache; | |
108 | ||
109 | if (!name) { | |
110 | list_for_each_entry(cache, &fscache_caches, cache_link) { | |
111 | if (cache->name && | |
112 | fscache_get_cache_maybe(cache, fscache_cache_get_acquire)) | |
113 | goto got_cache_w; | |
114 | } | |
115 | } | |
116 | ||
117 | list_add_tail(&candidate->cache_link, &fscache_caches); | |
118 | trace_fscache_cache(candidate->debug_id, | |
119 | refcount_read(&candidate->ref), | |
120 | fscache_cache_new_acquire); | |
121 | up_write(&fscache_addremove_sem); | |
122 | return candidate; | |
123 | ||
124 | got_cache_r: | |
125 | up_read(&fscache_addremove_sem); | |
126 | return cache; | |
127 | use_unnamed_cache: | |
128 | cache = unnamed; | |
129 | cache->name = candidate->name; | |
130 | candidate->name = NULL; | |
131 | got_cache_w: | |
132 | up_write(&fscache_addremove_sem); | |
133 | kfree(candidate->name); | |
134 | kfree(candidate); | |
135 | return cache; | |
136 | } | |
137 | ||
138 | /** | |
139 | * fscache_acquire_cache - Acquire a cache-level cookie. | |
140 | * @name: The name of the cache. | |
141 | * | |
142 | * Get a cookie to represent an actual cache. If a name is given and there is | |
143 | * a nameless cache record available, this will acquire that and set its name, | |
144 | * directing all the volumes using it to this cache. | |
145 | * | |
146 | * The cache will be switched over to the preparing state if not currently in | |
147 | * use, otherwise -EBUSY will be returned. | |
148 | */ | |
149 | struct fscache_cache *fscache_acquire_cache(const char *name) | |
150 | { | |
151 | struct fscache_cache *cache; | |
152 | ||
153 | ASSERT(name); | |
154 | cache = fscache_lookup_cache(name, true); | |
155 | if (IS_ERR(cache)) | |
156 | return cache; | |
157 | ||
158 | if (!fscache_set_cache_state_maybe(cache, | |
159 | FSCACHE_CACHE_IS_NOT_PRESENT, | |
160 | FSCACHE_CACHE_IS_PREPARING)) { | |
161 | pr_warn("Cache tag %s in use\n", name); | |
162 | fscache_put_cache(cache, fscache_cache_put_cache); | |
163 | return ERR_PTR(-EBUSY); | |
164 | } | |
165 | ||
166 | return cache; | |
167 | } | |
168 | EXPORT_SYMBOL(fscache_acquire_cache); | |
169 | ||
170 | /** | |
171 | * fscache_put_cache - Release a cache-level cookie. | |
172 | * @cache: The cache cookie to be released | |
173 | * @where: An indication of where the release happened | |
174 | * | |
175 | * Release the caller's reference on a cache-level cookie. The @where | |
176 | * indication should give information about the circumstances in which the call | |
177 | * occurs and will be logged through a tracepoint. | |
178 | */ | |
179 | void fscache_put_cache(struct fscache_cache *cache, | |
180 | enum fscache_cache_trace where) | |
181 | { | |
182 | unsigned int debug_id = cache->debug_id; | |
183 | bool zero; | |
184 | int ref; | |
185 | ||
186 | if (IS_ERR_OR_NULL(cache)) | |
187 | return; | |
188 | ||
189 | zero = __refcount_dec_and_test(&cache->ref, &ref); | |
190 | trace_fscache_cache(debug_id, ref - 1, where); | |
191 | ||
192 | if (zero) { | |
193 | down_write(&fscache_addremove_sem); | |
194 | list_del_init(&cache->cache_link); | |
195 | up_write(&fscache_addremove_sem); | |
196 | kfree(cache->name); | |
197 | kfree(cache); | |
198 | } | |
199 | } | |
200 | ||
201 | /** | |
202 | * fscache_relinquish_cache - Reset cache state and release cookie | |
203 | * @cache: The cache cookie to be released | |
204 | * | |
205 | * Reset the state of a cache and release the caller's reference on a cache | |
206 | * cookie. | |
207 | */ | |
208 | void fscache_relinquish_cache(struct fscache_cache *cache) | |
209 | { | |
210 | enum fscache_cache_trace where = | |
211 | (cache->state == FSCACHE_CACHE_IS_PREPARING) ? | |
212 | fscache_cache_put_prep_failed : | |
213 | fscache_cache_put_relinquish; | |
214 | ||
2e0c76ae | 215 | cache->ops = NULL; |
9549332d | 216 | cache->cache_priv = NULL; |
b3c958c2 | 217 | fscache_set_cache_state(cache, FSCACHE_CACHE_IS_NOT_PRESENT); |
9549332d DH |
218 | fscache_put_cache(cache, where); |
219 | } | |
220 | EXPORT_SYMBOL(fscache_relinquish_cache); | |
221 | ||
2e0c76ae DH |
222 | /** |
223 | * fscache_add_cache - Declare a cache as being open for business | |
224 | * @cache: The cache-level cookie representing the cache | |
225 | * @ops: Table of cache operations to use | |
226 | * @cache_priv: Private data for the cache record | |
227 | * | |
228 | * Add a cache to the system, making it available for netfs's to use. | |
229 | * | |
230 | * See Documentation/filesystems/caching/backend-api.rst for a complete | |
231 | * description. | |
232 | */ | |
233 | int fscache_add_cache(struct fscache_cache *cache, | |
234 | const struct fscache_cache_ops *ops, | |
235 | void *cache_priv) | |
236 | { | |
237 | int n_accesses; | |
238 | ||
239 | _enter("{%s,%s}", ops->name, cache->name); | |
240 | ||
241 | BUG_ON(fscache_cache_state(cache) != FSCACHE_CACHE_IS_PREPARING); | |
242 | ||
243 | /* Get a ref on the cache cookie and keep its n_accesses counter raised | |
244 | * by 1 to prevent wakeups from transitioning it to 0 until we're | |
245 | * withdrawing caching services from it. | |
246 | */ | |
247 | n_accesses = atomic_inc_return(&cache->n_accesses); | |
248 | trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), | |
249 | n_accesses, fscache_access_cache_pin); | |
250 | ||
251 | down_write(&fscache_addremove_sem); | |
252 | ||
253 | cache->ops = ops; | |
254 | cache->cache_priv = cache_priv; | |
255 | fscache_set_cache_state(cache, FSCACHE_CACHE_IS_ACTIVE); | |
256 | ||
257 | up_write(&fscache_addremove_sem); | |
258 | pr_notice("Cache \"%s\" added (type %s)\n", cache->name, ops->name); | |
259 | _leave(" = 0 [%s]", cache->name); | |
260 | return 0; | |
261 | } | |
262 | EXPORT_SYMBOL(fscache_add_cache); | |
263 | ||
23e12e28 DH |
264 | /** |
265 | * fscache_begin_cache_access - Pin a cache so it can be accessed | |
266 | * @cache: The cache-level cookie | |
267 | * @why: An indication of the circumstances of the access for tracing | |
268 | * | |
269 | * Attempt to pin the cache to prevent it from going away whilst we're | |
270 | * accessing it and returns true if successful. This works as follows: | |
271 | * | |
272 | * (1) If the cache tests as not live (state is not FSCACHE_CACHE_IS_ACTIVE), | |
273 | * then we return false to indicate access was not permitted. | |
274 | * | |
275 | * (2) If the cache tests as live, then we increment the n_accesses count and | |
276 | * then recheck the liveness, ending the access if it ceased to be live. | |
277 | * | |
278 | * (3) When we end the access, we decrement n_accesses and wake up the any | |
279 | * waiters if it reaches 0. | |
280 | * | |
281 | * (4) Whilst the cache is caching, n_accesses is kept artificially | |
282 | * incremented to prevent wakeups from happening. | |
283 | * | |
284 | * (5) When the cache is taken offline, the state is changed to prevent new | |
285 | * accesses, n_accesses is decremented and we wait for n_accesses to | |
286 | * become 0. | |
287 | */ | |
288 | bool fscache_begin_cache_access(struct fscache_cache *cache, enum fscache_access_trace why) | |
289 | { | |
290 | int n_accesses; | |
291 | ||
292 | if (!fscache_cache_is_live(cache)) | |
293 | return false; | |
294 | ||
295 | n_accesses = atomic_inc_return(&cache->n_accesses); | |
296 | smp_mb__after_atomic(); /* Reread live flag after n_accesses */ | |
297 | trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), | |
298 | n_accesses, why); | |
299 | if (!fscache_cache_is_live(cache)) { | |
300 | fscache_end_cache_access(cache, fscache_access_unlive); | |
301 | return false; | |
302 | } | |
303 | return true; | |
304 | } | |
305 | ||
306 | /** | |
307 | * fscache_end_cache_access - Unpin a cache at the end of an access. | |
308 | * @cache: The cache-level cookie | |
309 | * @why: An indication of the circumstances of the access for tracing | |
310 | * | |
311 | * Unpin a cache after we've accessed it. The @why indicator is merely | |
312 | * provided for tracing purposes. | |
313 | */ | |
314 | void fscache_end_cache_access(struct fscache_cache *cache, enum fscache_access_trace why) | |
315 | { | |
316 | int n_accesses; | |
317 | ||
318 | smp_mb__before_atomic(); | |
319 | n_accesses = atomic_dec_return(&cache->n_accesses); | |
320 | trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), | |
321 | n_accesses, why); | |
322 | if (n_accesses == 0) | |
323 | wake_up_var(&cache->n_accesses); | |
324 | } | |
325 | ||
29f18e79 DH |
326 | /** |
327 | * fscache_io_error - Note a cache I/O error | |
328 | * @cache: The record describing the cache | |
329 | * | |
330 | * Note that an I/O error occurred in a cache and that it should no longer be | |
331 | * used for anything. This also reports the error into the kernel log. | |
332 | * | |
333 | * See Documentation/filesystems/caching/backend-api.rst for a complete | |
334 | * description. | |
335 | */ | |
336 | void fscache_io_error(struct fscache_cache *cache) | |
337 | { | |
338 | if (fscache_set_cache_state_maybe(cache, | |
339 | FSCACHE_CACHE_IS_ACTIVE, | |
340 | FSCACHE_CACHE_GOT_IOERROR)) | |
341 | pr_err("Cache '%s' stopped due to I/O error\n", | |
342 | cache->name); | |
343 | } | |
344 | EXPORT_SYMBOL(fscache_io_error); | |
345 | ||
2e0c76ae DH |
346 | /** |
347 | * fscache_withdraw_cache - Withdraw a cache from the active service | |
348 | * @cache: The cache cookie | |
349 | * | |
350 | * Begin the process of withdrawing a cache from service. This stops new | |
351 | * cache-level and volume-level accesses from taking place and waits for | |
352 | * currently ongoing cache-level accesses to end. | |
353 | */ | |
354 | void fscache_withdraw_cache(struct fscache_cache *cache) | |
355 | { | |
356 | int n_accesses; | |
357 | ||
358 | pr_notice("Withdrawing cache \"%s\" (%u objs)\n", | |
359 | cache->name, atomic_read(&cache->object_count)); | |
360 | ||
361 | fscache_set_cache_state(cache, FSCACHE_CACHE_IS_WITHDRAWN); | |
362 | ||
363 | /* Allow wakeups on dec-to-0 */ | |
364 | n_accesses = atomic_dec_return(&cache->n_accesses); | |
365 | trace_fscache_access_cache(cache->debug_id, refcount_read(&cache->ref), | |
366 | n_accesses, fscache_access_cache_unpin); | |
367 | ||
368 | wait_var_event(&cache->n_accesses, | |
369 | atomic_read(&cache->n_accesses) == 0); | |
370 | } | |
371 | EXPORT_SYMBOL(fscache_withdraw_cache); | |
372 | ||
9549332d DH |
373 | #ifdef CONFIG_PROC_FS |
374 | static const char fscache_cache_states[NR__FSCACHE_CACHE_STATE] = "-PAEW"; | |
375 | ||
376 | /* | |
377 | * Generate a list of caches in /proc/fs/fscache/caches | |
378 | */ | |
379 | static int fscache_caches_seq_show(struct seq_file *m, void *v) | |
380 | { | |
381 | struct fscache_cache *cache; | |
382 | ||
383 | if (v == &fscache_caches) { | |
384 | seq_puts(m, | |
385 | "CACHE REF VOLS OBJS ACCES S NAME\n" | |
386 | "======== ===== ===== ===== ===== = ===============\n" | |
387 | ); | |
388 | return 0; | |
389 | } | |
390 | ||
391 | cache = list_entry(v, struct fscache_cache, cache_link); | |
392 | seq_printf(m, | |
393 | "%08x %5d %5d %5d %5d %c %s\n", | |
394 | cache->debug_id, | |
395 | refcount_read(&cache->ref), | |
396 | atomic_read(&cache->n_volumes), | |
397 | atomic_read(&cache->object_count), | |
398 | atomic_read(&cache->n_accesses), | |
399 | fscache_cache_states[cache->state], | |
400 | cache->name ?: "-"); | |
401 | return 0; | |
402 | } | |
403 | ||
404 | static void *fscache_caches_seq_start(struct seq_file *m, loff_t *_pos) | |
405 | __acquires(fscache_addremove_sem) | |
406 | { | |
407 | down_read(&fscache_addremove_sem); | |
408 | return seq_list_start_head(&fscache_caches, *_pos); | |
409 | } | |
410 | ||
411 | static void *fscache_caches_seq_next(struct seq_file *m, void *v, loff_t *_pos) | |
412 | { | |
413 | return seq_list_next(v, &fscache_caches, _pos); | |
414 | } | |
415 | ||
416 | static void fscache_caches_seq_stop(struct seq_file *m, void *v) | |
417 | __releases(fscache_addremove_sem) | |
418 | { | |
419 | up_read(&fscache_addremove_sem); | |
420 | } | |
421 | ||
422 | const struct seq_operations fscache_caches_seq_ops = { | |
423 | .start = fscache_caches_seq_start, | |
424 | .next = fscache_caches_seq_next, | |
425 | .stop = fscache_caches_seq_stop, | |
426 | .show = fscache_caches_seq_show, | |
427 | }; | |
428 | #endif /* CONFIG_PROC_FS */ |