stackdepot.c

  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/* Array of memory regions that store stack records. */
 65static void **stack_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(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 = kvcalloc(entries, sizeof(struct list_head), GFP_KERNEL);
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{
295	lockdep_assert_held(&pool_lock);
296
297	if (unlikely(pools_num >= stack_max_pools)) {
298		/* Bail out if we reached the pool limit. */
299		WARN_ON_ONCE(pools_num > stack_max_pools); /* should never happen */
300		WARN_ON_ONCE(!new_pool); /* to avoid unnecessary pre-allocation */
301		WARN_ONCE(1, "Stack depot reached limit capacity");
302		return false;
303	}
304
305	if (!new_pool && *prealloc) {
306		/* We have preallocated memory, use it. */
307		WRITE_ONCE(new_pool, *prealloc);
308		*prealloc = NULL;
309	}
310
311	if (!new_pool)
312		return false; /* new_pool and *prealloc are NULL */
313
314	/* Save reference to the pool to be used by depot_fetch_stack(). */
315	stack_pools[pools_num] = new_pool;
316
317	/*
318	 * Stack depot tries to keep an extra pool allocated even before it runs
319	 * out of space in the currently used pool.
320	 *
321	 * To indicate that a new preallocation is needed new_pool is reset to
322	 * NULL; do not reset to NULL if we have reached the maximum number of
323	 * pools.
324	 */
325	if (pools_num < stack_max_pools)
326		WRITE_ONCE(new_pool, NULL);
327	else
328		WRITE_ONCE(new_pool, STACK_DEPOT_POISON);
329
330	/* Pairs with concurrent READ_ONCE() in depot_fetch_stack(). */
331	WRITE_ONCE(pools_num, pools_num + 1);
332	ASSERT_EXCLUSIVE_WRITER(pools_num);
333
334	pool_offset = 0;
335
336	return true;
337}
338
339/* Keeps the preallocated memory to be used for a new stack depot pool. */
340static void depot_keep_new_pool(void **prealloc)
341{
342	lockdep_assert_held(&pool_lock);
343
344	/*
345	 * If a new pool is already saved or the maximum number of
346	 * pools is reached, do not use the preallocated memory.
347	 */
348	if (new_pool)
349		return;
350
351	WRITE_ONCE(new_pool, *prealloc);
352	*prealloc = NULL;
353}
354
355/*
356 * Try to initialize a new stack record from the current pool, a cached pool, or
357 * the current pre-allocation.
358 */
359static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
360{
361	struct stack_record *stack;
362	void *current_pool;
363	u32 pool_index;
364
365	lockdep_assert_held(&pool_lock);
366
367	if (pool_offset + size > DEPOT_POOL_SIZE) {
368		if (!depot_init_pool(prealloc))
369			return NULL;
370	}
371
372	if (WARN_ON_ONCE(pools_num < 1))
373		return NULL;
374	pool_index = pools_num - 1;
375	current_pool = stack_pools[pool_index];
376	if (WARN_ON_ONCE(!current_pool))
377		return NULL;
378
379	stack = current_pool + pool_offset;
380
381	/* Pre-initialize handle once. */
382	stack->handle.pool_index_plus_1 = pool_index + 1;
383	stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
384	stack->handle.extra = 0;
385	INIT_LIST_HEAD(&stack->hash_list);
386
387	pool_offset += size;
388
389	return stack;
390}
391
392/* Try to find next free usable entry from the freelist. */
393static struct stack_record *depot_pop_free(void)
394{
395	struct stack_record *stack;
396
397	lockdep_assert_held(&pool_lock);
398
399	if (list_empty(&free_stacks))
400		return NULL;
401
402	/*
403	 * We maintain the invariant that the elements in front are least
404	 * recently used, and are therefore more likely to be associated with an
405	 * RCU grace period in the past. Consequently it is sufficient to only
406	 * check the first entry.
407	 */
408	stack = list_first_entry(&free_stacks, struct stack_record, free_list);
409	if (!poll_state_synchronize_rcu(stack->rcu_state))
410		return NULL;
411
412	list_del(&stack->free_list);
413	counters[DEPOT_COUNTER_FREELIST_SIZE]--;
414
415	return stack;
416}
417
418static inline size_t depot_stack_record_size(struct stack_record *s, unsigned int nr_entries)
419{
420	const size_t used = flex_array_size(s, entries, nr_entries);
421	const size_t unused = sizeof(s->entries) - used;
422
423	WARN_ON_ONCE(sizeof(s->entries) < used);
424
425	return ALIGN(sizeof(struct stack_record) - unused, 1 << DEPOT_STACK_ALIGN);
426}
427
428/* Allocates a new stack in a stack depot pool. */
429static struct stack_record *
430depot_alloc_stack(unsigned long *entries, unsigned int nr_entries, u32 hash, depot_flags_t flags, void **prealloc)
431{
432	struct stack_record *stack = NULL;
433	size_t record_size;
434
435	lockdep_assert_held(&pool_lock);
436
437	/* This should already be checked by public API entry points. */
438	if (WARN_ON_ONCE(!nr_entries))
439		return NULL;
440
441	/* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */
442	if (nr_entries > CONFIG_STACKDEPOT_MAX_FRAMES)
443		nr_entries = CONFIG_STACKDEPOT_MAX_FRAMES;
444
445	if (flags & STACK_DEPOT_FLAG_GET) {
446		/*
447		 * Evictable entries have to allocate the max. size so they may
448		 * safely be re-used by differently sized allocations.
449		 */
450		record_size = depot_stack_record_size(stack, CONFIG_STACKDEPOT_MAX_FRAMES);
451		stack = depot_pop_free();
452	} else {
453		record_size = depot_stack_record_size(stack, nr_entries);
454	}
455
456	if (!stack) {
457		stack = depot_pop_free_pool(prealloc, record_size);
458		if (!stack)
459			return NULL;
460	}
461
462	/* Save the stack trace. */
463	stack->hash = hash;
464	stack->size = nr_entries;
465	/* stack->handle is already filled in by depot_pop_free_pool(). */
466	memcpy(stack->entries, entries, flex_array_size(stack, entries, nr_entries));
467
468	if (flags & STACK_DEPOT_FLAG_GET) {
469		refcount_set(&stack->count, 1);
470		counters[DEPOT_COUNTER_REFD_ALLOCS]++;
471		counters[DEPOT_COUNTER_REFD_INUSE]++;
472	} else {
473		/* Warn on attempts to switch to refcounting this entry. */
474		refcount_set(&stack->count, REFCOUNT_SATURATED);
475		counters[DEPOT_COUNTER_PERSIST_COUNT]++;
476		counters[DEPOT_COUNTER_PERSIST_BYTES] += record_size;
477	}
478
479	/*
480	 * Let KMSAN know the stored stack record is initialized. This shall
481	 * prevent false positive reports if instrumented code accesses it.
482	 */
483	kmsan_unpoison_memory(stack, record_size);
484
485	return stack;
486}
487
488static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
489{
490	const int pools_num_cached = READ_ONCE(pools_num);
491	union handle_parts parts = { .handle = handle };
492	void *pool;
493	u32 pool_index = parts.pool_index_plus_1 - 1;
494	size_t offset = parts.offset << DEPOT_STACK_ALIGN;
495	struct stack_record *stack;
496
497	lockdep_assert_not_held(&pool_lock);
498
499	if (pool_index >= pools_num_cached) {
500		WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
501		     pool_index, pools_num_cached, handle);
502		return NULL;
503	}
504
505	pool = stack_pools[pool_index];
506	if (WARN_ON(!pool))
507		return NULL;
508
509	stack = pool + offset;
510	if (WARN_ON(!refcount_read(&stack->count)))
511		return NULL;
512
513	return stack;
514}
515
516/* Links stack into the freelist. */
517static void depot_free_stack(struct stack_record *stack)
518{
519	unsigned long flags;
520
521	lockdep_assert_not_held(&pool_lock);
522
523	raw_spin_lock_irqsave(&pool_lock, flags);
524	printk_deferred_enter();
525
526	/*
527	 * Remove the entry from the hash list. Concurrent list traversal may
528	 * still observe the entry, but since the refcount is zero, this entry
529	 * will no longer be considered as valid.
530	 */
531	list_del_rcu(&stack->hash_list);
532
533	/*
534	 * Due to being used from constrained contexts such as the allocators,
535	 * NMI, or even RCU itself, stack depot cannot rely on primitives that
536	 * would sleep (such as synchronize_rcu()) or recursively call into
537	 * stack depot again (such as call_rcu()).
538	 *
539	 * Instead, get an RCU cookie, so that we can ensure this entry isn't
540	 * moved onto another list until the next grace period, and concurrent
541	 * RCU list traversal remains safe.
542	 */
543	stack->rcu_state = get_state_synchronize_rcu();
544
545	/*
546	 * Add the entry to the freelist tail, so that older entries are
547	 * considered first - their RCU cookie is more likely to no longer be
548	 * associated with the current grace period.
549	 */
550	list_add_tail(&stack->free_list, &free_stacks);
551
552	counters[DEPOT_COUNTER_FREELIST_SIZE]++;
553	counters[DEPOT_COUNTER_REFD_FREES]++;
554	counters[DEPOT_COUNTER_REFD_INUSE]--;
555
556	printk_deferred_exit();
557	raw_spin_unlock_irqrestore(&pool_lock, flags);
558}
559
560/* Calculates the hash for a stack. */
561static inline u32 hash_stack(unsigned long *entries, unsigned int size)
562{
563	return jhash2((u32 *)entries,
564		      array_size(size,  sizeof(*entries)) / sizeof(u32),
565		      STACK_HASH_SEED);
566}
567
568/*
569 * Non-instrumented version of memcmp().
570 * Does not check the lexicographical order, only the equality.
571 */
572static inline
573int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
574			unsigned int n)
575{
576	for ( ; n-- ; u1++, u2++) {
577		if (*u1 != *u2)
578			return 1;
579	}
580	return 0;
581}
582
583/* Finds a stack in a bucket of the hash table. */
584static inline struct stack_record *find_stack(struct list_head *bucket,
585					      unsigned long *entries, int size,
586					      u32 hash, depot_flags_t flags)
587{
588	struct stack_record *stack, *ret = NULL;
589
590	/*
591	 * Stack depot may be used from instrumentation that instruments RCU or
592	 * tracing itself; use variant that does not call into RCU and cannot be
593	 * traced.
594	 *
595	 * Note: Such use cases must take care when using refcounting to evict
596	 * unused entries, because the stack record free-then-reuse code paths
597	 * do call into RCU.
598	 */
599	rcu_read_lock_sched_notrace();
600
601	list_for_each_entry_rcu(stack, bucket, hash_list) {
602		if (stack->hash != hash || stack->size != size)
603			continue;
604
605		/*
606		 * This may race with depot_free_stack() accessing the freelist
607		 * management state unioned with @entries. The refcount is zero
608		 * in that case and the below refcount_inc_not_zero() will fail.
609		 */
610		if (data_race(stackdepot_memcmp(entries, stack->entries, size)))
611			continue;
612
613		/*
614		 * Try to increment refcount. If this succeeds, the stack record
615		 * is valid and has not yet been freed.
616		 *
617		 * If STACK_DEPOT_FLAG_GET is not used, it is undefined behavior
618		 * to then call stack_depot_put() later, and we can assume that
619		 * a stack record is never placed back on the freelist.
620		 */
621		if ((flags & STACK_DEPOT_FLAG_GET) && !refcount_inc_not_zero(&stack->count))
622			continue;
623
624		ret = stack;
625		break;
626	}
627
628	rcu_read_unlock_sched_notrace();
629
630	return ret;
631}
632
633depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
634					    unsigned int nr_entries,
635					    gfp_t alloc_flags,
636					    depot_flags_t depot_flags)
637{
638	struct list_head *bucket;
639	struct stack_record *found = NULL;
640	depot_stack_handle_t handle = 0;
641	struct page *page = NULL;
642	void *prealloc = NULL;
643	bool allow_spin = gfpflags_allow_spinning(alloc_flags);
644	bool can_alloc = (depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC) && allow_spin;
645	unsigned long flags;
646	u32 hash;
647
648	if (WARN_ON(depot_flags & ~STACK_DEPOT_FLAGS_MASK))
649		return 0;
650
651	/*
652	 * If this stack trace is from an interrupt, including anything before
653	 * interrupt entry usually leads to unbounded stack depot growth.
654	 *
655	 * Since use of filter_irq_stacks() is a requirement to ensure stack
656	 * depot can efficiently deduplicate interrupt stacks, always
657	 * filter_irq_stacks() to simplify all callers' use of stack depot.
658	 */
659	nr_entries = filter_irq_stacks(entries, nr_entries);
660
661	if (unlikely(nr_entries == 0) || stack_depot_disabled)
662		return 0;
663
664	hash = hash_stack(entries, nr_entries);
665	bucket = &stack_table[hash & stack_hash_mask];
666
667	/* Fast path: look the stack trace up without locking. */
668	found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
669	if (found)
670		goto exit;
671
672	/*
673	 * Allocate memory for a new pool if required now:
674	 * we won't be able to do that under the lock.
675	 */
676	if (unlikely(can_alloc && !READ_ONCE(new_pool))) {
677		page = alloc_pages(gfp_nested_mask(alloc_flags),
678				   DEPOT_POOL_ORDER);
679		if (page)
680			prealloc = page_address(page);
681	}
682
683	if (in_nmi() || !allow_spin) {
684		/* We can never allocate in NMI context. */
685		WARN_ON_ONCE(can_alloc);
686		/* Best effort; bail if we fail to take the lock. */
687		if (!raw_spin_trylock_irqsave(&pool_lock, flags))
688			goto exit;
689	} else {
690		raw_spin_lock_irqsave(&pool_lock, flags);
691	}
692	printk_deferred_enter();
693
694	/* Try to find again, to avoid concurrently inserting duplicates. */
695	found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
696	if (!found) {
697		struct stack_record *new =
698			depot_alloc_stack(entries, nr_entries, hash, depot_flags, &prealloc);
699
700		if (new) {
701			/*
702			 * This releases the stack record into the bucket and
703			 * makes it visible to readers in find_stack().
704			 */
705			list_add_rcu(&new->hash_list, bucket);
706			found = new;
707		}
708	}
709
710	if (prealloc) {
711		/*
712		 * Either stack depot already contains this stack trace, or
713		 * depot_alloc_stack() did not consume the preallocated memory.
714		 * Try to keep the preallocated memory for future.
715		 */
716		depot_keep_new_pool(&prealloc);
717	}
718
719	printk_deferred_exit();
720	raw_spin_unlock_irqrestore(&pool_lock, flags);
721exit:
722	if (prealloc) {
723		/* Stack depot didn't use this memory, free it. */
724		if (!allow_spin)
725			free_pages_nolock(virt_to_page(prealloc), DEPOT_POOL_ORDER);
726		else
727			free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
728	}
729	if (found)
730		handle = found->handle.handle;
731	return handle;
732}
733EXPORT_SYMBOL_GPL(stack_depot_save_flags);
734
735depot_stack_handle_t stack_depot_save(unsigned long *entries,
736				      unsigned int nr_entries,
737				      gfp_t alloc_flags)
738{
739	return stack_depot_save_flags(entries, nr_entries, alloc_flags,
740				      STACK_DEPOT_FLAG_CAN_ALLOC);
741}
742EXPORT_SYMBOL_GPL(stack_depot_save);
743
744struct stack_record *__stack_depot_get_stack_record(depot_stack_handle_t handle)
745{
746	if (!handle)
747		return NULL;
748
749	return depot_fetch_stack(handle);
750}
751
752unsigned int stack_depot_fetch(depot_stack_handle_t handle,
753			       unsigned long **entries)
754{
755	struct stack_record *stack;
756
757	*entries = NULL;
758	/*
759	 * Let KMSAN know *entries is initialized. This shall prevent false
760	 * positive reports if instrumented code accesses it.
761	 */
762	kmsan_unpoison_memory(entries, sizeof(*entries));
763
764	if (!handle || stack_depot_disabled)
765		return 0;
766
767	stack = depot_fetch_stack(handle);
768	/*
769	 * Should never be NULL, otherwise this is a use-after-put (or just a
770	 * corrupt handle).
771	 */
772	if (WARN(!stack, "corrupt handle or use after stack_depot_put()"))
773		return 0;
774
775	*entries = stack->entries;
776	return stack->size;
777}
778EXPORT_SYMBOL_GPL(stack_depot_fetch);
779
780void stack_depot_put(depot_stack_handle_t handle)
781{
782	struct stack_record *stack;
783
784	if (!handle || stack_depot_disabled)
785		return;
786
787	stack = depot_fetch_stack(handle);
788	/*
789	 * Should always be able to find the stack record, otherwise this is an
790	 * unbalanced put attempt (or corrupt handle).
791	 */
792	if (WARN(!stack, "corrupt handle or unbalanced stack_depot_put()"))
793		return;
794
795	if (refcount_dec_and_test(&stack->count))
796		depot_free_stack(stack);
797}
798EXPORT_SYMBOL_GPL(stack_depot_put);
799
800void stack_depot_print(depot_stack_handle_t stack)
801{
802	unsigned long *entries;
803	unsigned int nr_entries;
804
805	nr_entries = stack_depot_fetch(stack, &entries);
806	if (nr_entries > 0)
807		stack_trace_print(entries, nr_entries, 0);
808}
809EXPORT_SYMBOL_GPL(stack_depot_print);
810
811int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
812		       int spaces)
813{
814	unsigned long *entries;
815	unsigned int nr_entries;
816
817	nr_entries = stack_depot_fetch(handle, &entries);
818	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
819						spaces) : 0;
820}
821EXPORT_SYMBOL_GPL(stack_depot_snprint);
822
823depot_stack_handle_t __must_check stack_depot_set_extra_bits(
824			depot_stack_handle_t handle, unsigned int extra_bits)
825{
826	union handle_parts parts = { .handle = handle };
827
828	/* Don't set extra bits on empty handles. */
829	if (!handle)
830		return 0;
831
832	parts.extra = extra_bits;
833	return parts.handle;
834}
835EXPORT_SYMBOL(stack_depot_set_extra_bits);
836
837unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
838{
839	union handle_parts parts = { .handle = handle };
840
841	return parts.extra;
842}
843EXPORT_SYMBOL(stack_depot_get_extra_bits);
844
845static int stats_show(struct seq_file *seq, void *v)
846{
847	/*
848	 * data race ok: These are just statistics counters, and approximate
849	 * statistics are ok for debugging.
850	 */
851	seq_printf(seq, "pools: %d\n", data_race(pools_num));
852	for (int i = 0; i < DEPOT_COUNTER_COUNT; i++)
853		seq_printf(seq, "%s: %ld\n", counter_names[i], data_race(counters[i]));
854
855	return 0;
856}
857DEFINE_SHOW_ATTRIBUTE(stats);
858
859static int depot_debugfs_init(void)
860{
861	struct dentry *dir;
862
863	if (stack_depot_disabled)
864		return 0;
865
866	dir = debugfs_create_dir("stackdepot", NULL);
867	debugfs_create_file("stats", 0444, dir, NULL, &stats_fops);
868	return 0;
869}
870late_initcall(depot_debugfs_init);