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

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source code of linux/lib/stackdepot.c