Linux kernel mirror (for testing)
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linux
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Stack depot - a stack trace storage that avoids duplication.
4 *
5 * Internally, stack depot maintains a hash table of unique stacktraces. The
6 * stack traces themselves are stored contiguously one after another in a set
7 * of separate page allocations.
8 *
9 * Author: Alexander Potapenko <glider@google.com>
10 * Copyright (C) 2016 Google, Inc.
11 *
12 * Based on the code by Dmitry Chernenkov.
13 */
14
15#define pr_fmt(fmt) "stackdepot: " fmt
16
17#include <linux/debugfs.h>
18#include <linux/gfp.h>
19#include <linux/jhash.h>
20#include <linux/kernel.h>
21#include <linux/kmsan.h>
22#include <linux/list.h>
23#include <linux/mm.h>
24#include <linux/mutex.h>
25#include <linux/poison.h>
26#include <linux/printk.h>
27#include <linux/rculist.h>
28#include <linux/rcupdate.h>
29#include <linux/refcount.h>
30#include <linux/slab.h>
31#include <linux/spinlock.h>
32#include <linux/stacktrace.h>
33#include <linux/stackdepot.h>
34#include <linux/string.h>
35#include <linux/types.h>
36#include <linux/memblock.h>
37#include <linux/kasan-enabled.h>
38
39/*
40 * The pool_index is offset by 1 so the first record does not have a 0 handle.
41 */
42static unsigned int stack_max_pools __read_mostly =
43 MIN((1LL << DEPOT_POOL_INDEX_BITS) - 1, 8192);
44
45static bool stack_depot_disabled;
46static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
47static bool __stack_depot_early_init_passed __initdata;
48
49/* Use one hash table bucket per 16 KB of memory. */
50#define STACK_HASH_TABLE_SCALE 14
51/* Limit the number of buckets between 4K and 1M. */
52#define STACK_BUCKET_NUMBER_ORDER_MIN 12
53#define STACK_BUCKET_NUMBER_ORDER_MAX 20
54/* Initial seed for jhash2. */
55#define STACK_HASH_SEED 0x9747b28c
56
57/* Hash table of stored stack records. */
58static struct list_head *stack_table;
59/* Fixed order of the number of table buckets. Used when KASAN is enabled. */
60static unsigned int stack_bucket_number_order;
61/* Hash mask for indexing the table. */
62static unsigned int stack_hash_mask;
63
64/* The lock must be held when performing pool or freelist modifications. */
65static DEFINE_RAW_SPINLOCK(pool_lock);
66/* Array of memory regions that store stack records. */
67static void **stack_pools __pt_guarded_by(&pool_lock);
68/* Newly allocated pool that is not yet added to stack_pools. */
69static void *new_pool;
70/* Number of pools in stack_pools. */
71static int pools_num;
72/* Offset to the unused space in the currently used pool. */
73static size_t pool_offset __guarded_by(&pool_lock) = DEPOT_POOL_SIZE;
74/* Freelist of stack records within stack_pools. */
75static __guarded_by(&pool_lock) LIST_HEAD(free_stacks);
76
77/* Statistics counters for debugfs. */
78enum depot_counter_id {
79 DEPOT_COUNTER_REFD_ALLOCS,
80 DEPOT_COUNTER_REFD_FREES,
81 DEPOT_COUNTER_REFD_INUSE,
82 DEPOT_COUNTER_FREELIST_SIZE,
83 DEPOT_COUNTER_PERSIST_COUNT,
84 DEPOT_COUNTER_PERSIST_BYTES,
85 DEPOT_COUNTER_COUNT,
86};
87static long counters[DEPOT_COUNTER_COUNT];
88static const char *const counter_names[] = {
89 [DEPOT_COUNTER_REFD_ALLOCS] = "refcounted_allocations",
90 [DEPOT_COUNTER_REFD_FREES] = "refcounted_frees",
91 [DEPOT_COUNTER_REFD_INUSE] = "refcounted_in_use",
92 [DEPOT_COUNTER_FREELIST_SIZE] = "freelist_size",
93 [DEPOT_COUNTER_PERSIST_COUNT] = "persistent_count",
94 [DEPOT_COUNTER_PERSIST_BYTES] = "persistent_bytes",
95};
96static_assert(ARRAY_SIZE(counter_names) == DEPOT_COUNTER_COUNT);
97
98static int __init disable_stack_depot(char *str)
99{
100 return kstrtobool(str, &stack_depot_disabled);
101}
102early_param("stack_depot_disable", disable_stack_depot);
103
104static int __init parse_max_pools(char *str)
105{
106 const long long limit = (1LL << (DEPOT_POOL_INDEX_BITS)) - 1;
107 unsigned int max_pools;
108 int rv;
109
110 rv = kstrtouint(str, 0, &max_pools);
111 if (rv)
112 return rv;
113
114 if (max_pools < 1024) {
115 pr_err("stack_depot_max_pools below 1024, using default of %u\n",
116 stack_max_pools);
117 goto out;
118 }
119
120 if (max_pools > limit) {
121 pr_err("stack_depot_max_pools exceeds %lld, using default of %u\n",
122 limit, stack_max_pools);
123 goto out;
124 }
125
126 stack_max_pools = max_pools;
127out:
128 return 0;
129}
130early_param("stack_depot_max_pools", parse_max_pools);
131
132void __init stack_depot_request_early_init(void)
133{
134 /* Too late to request early init now. */
135 WARN_ON(__stack_depot_early_init_passed);
136
137 __stack_depot_early_init_requested = true;
138}
139
140/* Initialize list_head's within the hash table. */
141static void init_stack_table(unsigned long entries)
142{
143 unsigned long i;
144
145 for (i = 0; i < entries; i++)
146 INIT_LIST_HEAD(&stack_table[i]);
147}
148
149/* Allocates a hash table via memblock. Can only be used during early boot. */
150int __init stack_depot_early_init(void)
151{
152 unsigned long entries = 0;
153
154 /* This function must be called only once, from mm_init(). */
155 if (WARN_ON(__stack_depot_early_init_passed))
156 return 0;
157 __stack_depot_early_init_passed = true;
158
159 /*
160 * Print disabled message even if early init has not been requested:
161 * stack_depot_init() will not print one.
162 */
163 if (stack_depot_disabled) {
164 pr_info("disabled\n");
165 return 0;
166 }
167
168 /*
169 * If KASAN is enabled, use the maximum order: KASAN is frequently used
170 * in fuzzing scenarios, which leads to a large number of different
171 * stack traces being stored in stack depot.
172 */
173 if (kasan_enabled() && !stack_bucket_number_order)
174 stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX;
175
176 /*
177 * Check if early init has been requested after setting
178 * stack_bucket_number_order: stack_depot_init() uses its value.
179 */
180 if (!__stack_depot_early_init_requested)
181 return 0;
182
183 /*
184 * If stack_bucket_number_order is not set, leave entries as 0 to rely
185 * on the automatic calculations performed by alloc_large_system_hash().
186 */
187 if (stack_bucket_number_order)
188 entries = 1UL << stack_bucket_number_order;
189 pr_info("allocating hash table via alloc_large_system_hash\n");
190 stack_table = alloc_large_system_hash("stackdepot",
191 sizeof(struct list_head),
192 entries,
193 STACK_HASH_TABLE_SCALE,
194 HASH_EARLY,
195 NULL,
196 &stack_hash_mask,
197 1UL << STACK_BUCKET_NUMBER_ORDER_MIN,
198 1UL << STACK_BUCKET_NUMBER_ORDER_MAX);
199 if (!stack_table) {
200 pr_err("hash table allocation failed, disabling\n");
201 stack_depot_disabled = true;
202 return -ENOMEM;
203 }
204 if (!entries) {
205 /*
206 * Obtain the number of entries that was calculated by
207 * alloc_large_system_hash().
208 */
209 entries = stack_hash_mask + 1;
210 }
211 init_stack_table(entries);
212
213 pr_info("allocating space for %u stack pools via memblock\n",
214 stack_max_pools);
215 stack_pools =
216 memblock_alloc(stack_max_pools * sizeof(void *), PAGE_SIZE);
217 if (!stack_pools) {
218 pr_err("stack pools allocation failed, disabling\n");
219 memblock_free(stack_table, entries * sizeof(struct list_head));
220 stack_depot_disabled = true;
221 return -ENOMEM;
222 }
223
224 return 0;
225}
226
227/* Allocates a hash table via kvcalloc. Can be used after boot. */
228int stack_depot_init(void)
229{
230 static DEFINE_MUTEX(stack_depot_init_mutex);
231 unsigned long entries;
232 int ret = 0;
233
234 mutex_lock(&stack_depot_init_mutex);
235
236 if (stack_depot_disabled || stack_table)
237 goto out_unlock;
238
239 /*
240 * Similarly to stack_depot_early_init, use stack_bucket_number_order
241 * if assigned, and rely on automatic scaling otherwise.
242 */
243 if (stack_bucket_number_order) {
244 entries = 1UL << stack_bucket_number_order;
245 } else {
246 int scale = STACK_HASH_TABLE_SCALE;
247
248 entries = nr_free_buffer_pages();
249 entries = roundup_pow_of_two(entries);
250
251 if (scale > PAGE_SHIFT)
252 entries >>= (scale - PAGE_SHIFT);
253 else
254 entries <<= (PAGE_SHIFT - scale);
255 }
256
257 if (entries < 1UL << STACK_BUCKET_NUMBER_ORDER_MIN)
258 entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MIN;
259 if (entries > 1UL << STACK_BUCKET_NUMBER_ORDER_MAX)
260 entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MAX;
261
262 pr_info("allocating hash table of %lu entries via kvcalloc\n", entries);
263 stack_table = kvzalloc_objs(struct list_head, entries);
264 if (!stack_table) {
265 pr_err("hash table allocation failed, disabling\n");
266 stack_depot_disabled = true;
267 ret = -ENOMEM;
268 goto out_unlock;
269 }
270 stack_hash_mask = entries - 1;
271 init_stack_table(entries);
272
273 pr_info("allocating space for %u stack pools via kvcalloc\n",
274 stack_max_pools);
275 stack_pools = kvcalloc(stack_max_pools, sizeof(void *), GFP_KERNEL);
276 if (!stack_pools) {
277 pr_err("stack pools allocation failed, disabling\n");
278 kvfree(stack_table);
279 stack_depot_disabled = true;
280 ret = -ENOMEM;
281 }
282
283out_unlock:
284 mutex_unlock(&stack_depot_init_mutex);
285
286 return ret;
287}
288EXPORT_SYMBOL_GPL(stack_depot_init);
289
290/*
291 * Initializes new stack pool, and updates the list of pools.
292 */
293static bool depot_init_pool(void **prealloc)
294 __must_hold(&pool_lock)
295{
296 lockdep_assert_held(&pool_lock);
297
298 if (unlikely(pools_num >= stack_max_pools)) {
299 /* Bail out if we reached the pool limit. */
300 WARN_ON_ONCE(pools_num > stack_max_pools); /* should never happen */
301 WARN_ON_ONCE(!new_pool); /* to avoid unnecessary pre-allocation */
302 WARN_ONCE(1, "Stack depot reached limit capacity");
303 return false;
304 }
305
306 if (!new_pool && *prealloc) {
307 /* We have preallocated memory, use it. */
308 WRITE_ONCE(new_pool, *prealloc);
309 *prealloc = NULL;
310 }
311
312 if (!new_pool)
313 return false; /* new_pool and *prealloc are NULL */
314
315 /* Save reference to the pool to be used by depot_fetch_stack(). */
316 stack_pools[pools_num] = new_pool;
317
318 /*
319 * Stack depot tries to keep an extra pool allocated even before it runs
320 * out of space in the currently used pool.
321 *
322 * To indicate that a new preallocation is needed new_pool is reset to
323 * NULL; do not reset to NULL if we have reached the maximum number of
324 * pools.
325 */
326 if (pools_num < stack_max_pools)
327 WRITE_ONCE(new_pool, NULL);
328 else
329 WRITE_ONCE(new_pool, STACK_DEPOT_POISON);
330
331 /* Pairs with concurrent READ_ONCE() in depot_fetch_stack(). */
332 WRITE_ONCE(pools_num, pools_num + 1);
333 ASSERT_EXCLUSIVE_WRITER(pools_num);
334
335 pool_offset = 0;
336
337 return true;
338}
339
340/* Keeps the preallocated memory to be used for a new stack depot pool. */
341static void depot_keep_new_pool(void **prealloc)
342 __must_hold(&pool_lock)
343{
344 lockdep_assert_held(&pool_lock);
345
346 /*
347 * If a new pool is already saved or the maximum number of
348 * pools is reached, do not use the preallocated memory.
349 */
350 if (new_pool)
351 return;
352
353 WRITE_ONCE(new_pool, *prealloc);
354 *prealloc = NULL;
355}
356
357/*
358 * Try to initialize a new stack record from the current pool, a cached pool, or
359 * the current pre-allocation.
360 */
361static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
362 __must_hold(&pool_lock)
363{
364 struct stack_record *stack;
365 void *current_pool;
366 u32 pool_index;
367
368 lockdep_assert_held(&pool_lock);
369
370 if (pool_offset + size > DEPOT_POOL_SIZE) {
371 if (!depot_init_pool(prealloc))
372 return NULL;
373 }
374
375 if (WARN_ON_ONCE(pools_num < 1))
376 return NULL;
377 pool_index = pools_num - 1;
378 current_pool = stack_pools[pool_index];
379 if (WARN_ON_ONCE(!current_pool))
380 return NULL;
381
382 stack = current_pool + pool_offset;
383
384 /* Pre-initialize handle once. */
385 stack->handle.pool_index_plus_1 = pool_index + 1;
386 stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
387 stack->handle.extra = 0;
388 INIT_LIST_HEAD(&stack->hash_list);
389
390 pool_offset += size;
391
392 return stack;
393}
394
395/* Try to find next free usable entry from the freelist. */
396static struct stack_record *depot_pop_free(void)
397 __must_hold(&pool_lock)
398{
399 struct stack_record *stack;
400
401 lockdep_assert_held(&pool_lock);
402
403 if (list_empty(&free_stacks))
404 return NULL;
405
406 /*
407 * We maintain the invariant that the elements in front are least
408 * recently used, and are therefore more likely to be associated with an
409 * RCU grace period in the past. Consequently it is sufficient to only
410 * check the first entry.
411 */
412 stack = list_first_entry(&free_stacks, struct stack_record, free_list);
413 if (!poll_state_synchronize_rcu(stack->rcu_state))
414 return NULL;
415
416 list_del(&stack->free_list);
417 counters[DEPOT_COUNTER_FREELIST_SIZE]--;
418
419 return stack;
420}
421
422static inline size_t depot_stack_record_size(struct stack_record *s, unsigned int nr_entries)
423{
424 const size_t used = flex_array_size(s, entries, nr_entries);
425 const size_t unused = sizeof(s->entries) - used;
426
427 WARN_ON_ONCE(sizeof(s->entries) < used);
428
429 return ALIGN(sizeof(struct stack_record) - unused, 1 << DEPOT_STACK_ALIGN);
430}
431
432/* Allocates a new stack in a stack depot pool. */
433static struct stack_record *
434depot_alloc_stack(unsigned long *entries, unsigned int nr_entries, u32 hash, depot_flags_t flags, void **prealloc)
435 __must_hold(&pool_lock)
436{
437 struct stack_record *stack = NULL;
438 size_t record_size;
439
440 lockdep_assert_held(&pool_lock);
441
442 /* This should already be checked by public API entry points. */
443 if (WARN_ON_ONCE(!nr_entries))
444 return NULL;
445
446 /* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */
447 if (nr_entries > CONFIG_STACKDEPOT_MAX_FRAMES)
448 nr_entries = CONFIG_STACKDEPOT_MAX_FRAMES;
449
450 if (flags & STACK_DEPOT_FLAG_GET) {
451 /*
452 * Evictable entries have to allocate the max. size so they may
453 * safely be re-used by differently sized allocations.
454 */
455 record_size = depot_stack_record_size(stack, CONFIG_STACKDEPOT_MAX_FRAMES);
456 stack = depot_pop_free();
457 } else {
458 record_size = depot_stack_record_size(stack, nr_entries);
459 }
460
461 if (!stack) {
462 stack = depot_pop_free_pool(prealloc, record_size);
463 if (!stack)
464 return NULL;
465 }
466
467 /* Save the stack trace. */
468 stack->hash = hash;
469 stack->size = nr_entries;
470 /* stack->handle is already filled in by depot_pop_free_pool(). */
471 memcpy(stack->entries, entries, flex_array_size(stack, entries, nr_entries));
472
473 if (flags & STACK_DEPOT_FLAG_GET) {
474 refcount_set(&stack->count, 1);
475 counters[DEPOT_COUNTER_REFD_ALLOCS]++;
476 counters[DEPOT_COUNTER_REFD_INUSE]++;
477 } else {
478 /* Warn on attempts to switch to refcounting this entry. */
479 refcount_set(&stack->count, REFCOUNT_SATURATED);
480 counters[DEPOT_COUNTER_PERSIST_COUNT]++;
481 counters[DEPOT_COUNTER_PERSIST_BYTES] += record_size;
482 }
483
484 /*
485 * Let KMSAN know the stored stack record is initialized. This shall
486 * prevent false positive reports if instrumented code accesses it.
487 */
488 kmsan_unpoison_memory(stack, record_size);
489
490 return stack;
491}
492
493static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
494 __must_not_hold(&pool_lock)
495{
496 const int pools_num_cached = READ_ONCE(pools_num);
497 union handle_parts parts = { .handle = handle };
498 void *pool;
499 u32 pool_index = parts.pool_index_plus_1 - 1;
500 size_t offset = parts.offset << DEPOT_STACK_ALIGN;
501 struct stack_record *stack;
502
503 lockdep_assert_not_held(&pool_lock);
504
505 if (pool_index >= pools_num_cached) {
506 WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
507 pool_index, pools_num_cached, handle);
508 return NULL;
509 }
510
511 /* @pool_index either valid, or user passed in corrupted value. */
512 pool = context_unsafe(stack_pools[pool_index]);
513 if (WARN_ON(!pool))
514 return NULL;
515
516 stack = pool + offset;
517 if (WARN_ON(!refcount_read(&stack->count)))
518 return NULL;
519
520 return stack;
521}
522
523/* Links stack into the freelist. */
524static void depot_free_stack(struct stack_record *stack)
525 __must_not_hold(&pool_lock)
526{
527 unsigned long flags;
528
529 lockdep_assert_not_held(&pool_lock);
530
531 raw_spin_lock_irqsave(&pool_lock, flags);
532 printk_deferred_enter();
533
534 /*
535 * Remove the entry from the hash list. Concurrent list traversal may
536 * still observe the entry, but since the refcount is zero, this entry
537 * will no longer be considered as valid.
538 */
539 list_del_rcu(&stack->hash_list);
540
541 /*
542 * Due to being used from constrained contexts such as the allocators,
543 * NMI, or even RCU itself, stack depot cannot rely on primitives that
544 * would sleep (such as synchronize_rcu()) or recursively call into
545 * stack depot again (such as call_rcu()).
546 *
547 * Instead, get an RCU cookie, so that we can ensure this entry isn't
548 * moved onto another list until the next grace period, and concurrent
549 * RCU list traversal remains safe.
550 */
551 stack->rcu_state = get_state_synchronize_rcu();
552
553 /*
554 * Add the entry to the freelist tail, so that older entries are
555 * considered first - their RCU cookie is more likely to no longer be
556 * associated with the current grace period.
557 */
558 list_add_tail(&stack->free_list, &free_stacks);
559
560 counters[DEPOT_COUNTER_FREELIST_SIZE]++;
561 counters[DEPOT_COUNTER_REFD_FREES]++;
562 counters[DEPOT_COUNTER_REFD_INUSE]--;
563
564 printk_deferred_exit();
565 raw_spin_unlock_irqrestore(&pool_lock, flags);
566}
567
568/* Calculates the hash for a stack. */
569static inline u32 hash_stack(unsigned long *entries, unsigned int size)
570{
571 return jhash2((u32 *)entries,
572 array_size(size, sizeof(*entries)) / sizeof(u32),
573 STACK_HASH_SEED);
574}
575
576/*
577 * Non-instrumented version of memcmp().
578 * Does not check the lexicographical order, only the equality.
579 */
580static inline
581int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
582 unsigned int n)
583{
584 for ( ; n-- ; u1++, u2++) {
585 if (*u1 != *u2)
586 return 1;
587 }
588 return 0;
589}
590
591/* Finds a stack in a bucket of the hash table. */
592static inline struct stack_record *find_stack(struct list_head *bucket,
593 unsigned long *entries, int size,
594 u32 hash, depot_flags_t flags)
595{
596 struct stack_record *stack, *ret = NULL;
597
598 /*
599 * Stack depot may be used from instrumentation that instruments RCU or
600 * tracing itself; use variant that does not call into RCU and cannot be
601 * traced.
602 *
603 * Note: Such use cases must take care when using refcounting to evict
604 * unused entries, because the stack record free-then-reuse code paths
605 * do call into RCU.
606 */
607 rcu_read_lock_sched_notrace();
608
609 list_for_each_entry_rcu(stack, bucket, hash_list) {
610 if (stack->hash != hash || stack->size != size)
611 continue;
612
613 /*
614 * This may race with depot_free_stack() accessing the freelist
615 * management state unioned with @entries. The refcount is zero
616 * in that case and the below refcount_inc_not_zero() will fail.
617 */
618 if (data_race(stackdepot_memcmp(entries, stack->entries, size)))
619 continue;
620
621 /*
622 * Try to increment refcount. If this succeeds, the stack record
623 * is valid and has not yet been freed.
624 *
625 * If STACK_DEPOT_FLAG_GET is not used, it is undefined behavior
626 * to then call stack_depot_put() later, and we can assume that
627 * a stack record is never placed back on the freelist.
628 */
629 if ((flags & STACK_DEPOT_FLAG_GET) && !refcount_inc_not_zero(&stack->count))
630 continue;
631
632 ret = stack;
633 break;
634 }
635
636 rcu_read_unlock_sched_notrace();
637
638 return ret;
639}
640
641depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
642 unsigned int nr_entries,
643 gfp_t alloc_flags,
644 depot_flags_t depot_flags)
645{
646 struct list_head *bucket;
647 struct stack_record *found = NULL;
648 depot_stack_handle_t handle = 0;
649 struct page *page = NULL;
650 void *prealloc = NULL;
651 bool allow_spin = gfpflags_allow_spinning(alloc_flags);
652 bool can_alloc = (depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC) && allow_spin;
653 unsigned long flags;
654 u32 hash;
655
656 if (WARN_ON(depot_flags & ~STACK_DEPOT_FLAGS_MASK))
657 return 0;
658
659 /*
660 * If this stack trace is from an interrupt, including anything before
661 * interrupt entry usually leads to unbounded stack depot growth.
662 *
663 * Since use of filter_irq_stacks() is a requirement to ensure stack
664 * depot can efficiently deduplicate interrupt stacks, always
665 * filter_irq_stacks() to simplify all callers' use of stack depot.
666 */
667 nr_entries = filter_irq_stacks(entries, nr_entries);
668
669 if (unlikely(nr_entries == 0) || stack_depot_disabled)
670 return 0;
671
672 hash = hash_stack(entries, nr_entries);
673 bucket = &stack_table[hash & stack_hash_mask];
674
675 /* Fast path: look the stack trace up without locking. */
676 found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
677 if (found)
678 goto exit;
679
680 /*
681 * Allocate memory for a new pool if required now:
682 * we won't be able to do that under the lock.
683 */
684 if (unlikely(can_alloc && !READ_ONCE(new_pool))) {
685 page = alloc_pages(gfp_nested_mask(alloc_flags),
686 DEPOT_POOL_ORDER);
687 if (page)
688 prealloc = page_address(page);
689 }
690
691 if (in_nmi() || !allow_spin) {
692 /* We can never allocate in NMI context. */
693 WARN_ON_ONCE(can_alloc);
694 /* Best effort; bail if we fail to take the lock. */
695 if (!raw_spin_trylock_irqsave(&pool_lock, flags))
696 goto exit;
697 } else {
698 raw_spin_lock_irqsave(&pool_lock, flags);
699 }
700 printk_deferred_enter();
701
702 /* Try to find again, to avoid concurrently inserting duplicates. */
703 found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
704 if (!found) {
705 struct stack_record *new =
706 depot_alloc_stack(entries, nr_entries, hash, depot_flags, &prealloc);
707
708 if (new) {
709 /*
710 * This releases the stack record into the bucket and
711 * makes it visible to readers in find_stack().
712 */
713 list_add_rcu(&new->hash_list, bucket);
714 found = new;
715 }
716 }
717
718 if (prealloc) {
719 /*
720 * Either stack depot already contains this stack trace, or
721 * depot_alloc_stack() did not consume the preallocated memory.
722 * Try to keep the preallocated memory for future.
723 */
724 depot_keep_new_pool(&prealloc);
725 }
726
727 printk_deferred_exit();
728 raw_spin_unlock_irqrestore(&pool_lock, flags);
729exit:
730 if (prealloc) {
731 /* Stack depot didn't use this memory, free it. */
732 if (!allow_spin)
733 free_pages_nolock(virt_to_page(prealloc), DEPOT_POOL_ORDER);
734 else
735 free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
736 }
737 if (found)
738 handle = found->handle.handle;
739 return handle;
740}
741EXPORT_SYMBOL_GPL(stack_depot_save_flags);
742
743depot_stack_handle_t stack_depot_save(unsigned long *entries,
744 unsigned int nr_entries,
745 gfp_t alloc_flags)
746{
747 return stack_depot_save_flags(entries, nr_entries, alloc_flags,
748 STACK_DEPOT_FLAG_CAN_ALLOC);
749}
750EXPORT_SYMBOL_GPL(stack_depot_save);
751
752struct stack_record *__stack_depot_get_stack_record(depot_stack_handle_t handle)
753{
754 if (!handle)
755 return NULL;
756
757 return depot_fetch_stack(handle);
758}
759
760unsigned int stack_depot_fetch(depot_stack_handle_t handle,
761 unsigned long **entries)
762{
763 struct stack_record *stack;
764
765 *entries = NULL;
766 /*
767 * Let KMSAN know *entries is initialized. This shall prevent false
768 * positive reports if instrumented code accesses it.
769 */
770 kmsan_unpoison_memory(entries, sizeof(*entries));
771
772 if (!handle || stack_depot_disabled)
773 return 0;
774
775 stack = depot_fetch_stack(handle);
776 /*
777 * Should never be NULL, otherwise this is a use-after-put (or just a
778 * corrupt handle).
779 */
780 if (WARN(!stack, "corrupt handle or use after stack_depot_put()"))
781 return 0;
782
783 *entries = stack->entries;
784 return stack->size;
785}
786EXPORT_SYMBOL_GPL(stack_depot_fetch);
787
788void stack_depot_put(depot_stack_handle_t handle)
789{
790 struct stack_record *stack;
791
792 if (!handle || stack_depot_disabled)
793 return;
794
795 stack = depot_fetch_stack(handle);
796 /*
797 * Should always be able to find the stack record, otherwise this is an
798 * unbalanced put attempt (or corrupt handle).
799 */
800 if (WARN(!stack, "corrupt handle or unbalanced stack_depot_put()"))
801 return;
802
803 if (refcount_dec_and_test(&stack->count))
804 depot_free_stack(stack);
805}
806EXPORT_SYMBOL_GPL(stack_depot_put);
807
808void stack_depot_print(depot_stack_handle_t stack)
809{
810 unsigned long *entries;
811 unsigned int nr_entries;
812
813 nr_entries = stack_depot_fetch(stack, &entries);
814 if (nr_entries > 0)
815 stack_trace_print(entries, nr_entries, 0);
816}
817EXPORT_SYMBOL_GPL(stack_depot_print);
818
819int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
820 int spaces)
821{
822 unsigned long *entries;
823 unsigned int nr_entries;
824
825 nr_entries = stack_depot_fetch(handle, &entries);
826 return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
827 spaces) : 0;
828}
829EXPORT_SYMBOL_GPL(stack_depot_snprint);
830
831depot_stack_handle_t __must_check stack_depot_set_extra_bits(
832 depot_stack_handle_t handle, unsigned int extra_bits)
833{
834 union handle_parts parts = { .handle = handle };
835
836 /* Don't set extra bits on empty handles. */
837 if (!handle)
838 return 0;
839
840 parts.extra = extra_bits;
841 return parts.handle;
842}
843EXPORT_SYMBOL(stack_depot_set_extra_bits);
844
845unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
846{
847 union handle_parts parts = { .handle = handle };
848
849 return parts.extra;
850}
851EXPORT_SYMBOL(stack_depot_get_extra_bits);
852
853static int stats_show(struct seq_file *seq, void *v)
854{
855 /*
856 * data race ok: These are just statistics counters, and approximate
857 * statistics are ok for debugging.
858 */
859 seq_printf(seq, "pools: %d\n", data_race(pools_num));
860 for (int i = 0; i < DEPOT_COUNTER_COUNT; i++)
861 seq_printf(seq, "%s: %ld\n", counter_names[i], data_race(counters[i]));
862
863 return 0;
864}
865DEFINE_SHOW_ATTRIBUTE(stats);
866
867static int depot_debugfs_init(void)
868{
869 struct dentry *dir;
870
871 if (stack_depot_disabled)
872 return 0;
873
874 dir = debugfs_create_dir("stackdepot", NULL);
875 debugfs_create_file("stats", 0444, dir, NULL, &stats_fops);
876 return 0;
877}
878late_initcall(depot_debugfs_init);