lib/stackdepot.c - fs/xfs/xfs-linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Stack depot - a stack trace storage that avoids duplication.
  *
  * Internally, stack depot maintains a hash table of unique stacktraces. The
  * stack traces themselves are stored contiguously one after another in a set
  * of separate page allocations.
  *
  * Author: Alexander Potapenko <glider@google.com>
  * Copyright (C) 2016 Google, Inc.
  *
  * Based on the code by Dmitry Chernenkov.
  */

 #define pr_fmt(fmt) "stackdepot: " fmt

 #include <linux/gfp.h>
 #include <linux/jhash.h>
 #include <linux/kernel.h>
 #include <linux/kmsan.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/percpu.h>
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/stacktrace.h>
 #include <linux/stackdepot.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/memblock.h>
 #include <linux/kasan-enabled.h>

 #define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)

 #define DEPOT_VALID_BITS 1
 #define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
 #define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
 #define DEPOT_STACK_ALIGN 4
 #define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
 #define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_VALID_BITS - \
 			       DEPOT_OFFSET_BITS - STACK_DEPOT_EXTRA_BITS)
 #define DEPOT_POOLS_CAP 8192
 #define DEPOT_MAX_POOLS \
 	(((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
 	 (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)

 /* Compact structure that stores a reference to a stack. */
 union handle_parts {
 	depot_stack_handle_t handle;
 	struct {
 		u32 pool_index	: DEPOT_POOL_INDEX_BITS;
 		u32 offset	: DEPOT_OFFSET_BITS;
 		u32 valid	: DEPOT_VALID_BITS;
 		u32 extra	: STACK_DEPOT_EXTRA_BITS;
 	};
 };

 struct stack_record {
 	struct stack_record *next;	/* Link in the hash table */
 	u32 hash;			/* Hash in the hash table */
 	u32 size;			/* Number of stored frames */
 	union handle_parts handle;
 	unsigned long entries[];	/* Variable-sized array of frames */
 };

 static bool stack_depot_disabled;
 static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
 static bool __stack_depot_early_init_passed __initdata;

 /* Use one hash table bucket per 16 KB of memory. */
 #define STACK_HASH_TABLE_SCALE 14
 /* Limit the number of buckets between 4K and 1M. */
 #define STACK_BUCKET_NUMBER_ORDER_MIN 12
 #define STACK_BUCKET_NUMBER_ORDER_MAX 20
 /* Initial seed for jhash2. */
 #define STACK_HASH_SEED 0x9747b28c

 /* Hash table of pointers to stored stack traces. */
 static struct stack_record **stack_table;
 /* Fixed order of the number of table buckets. Used when KASAN is enabled. */
 static unsigned int stack_bucket_number_order;
 /* Hash mask for indexing the table. */
 static unsigned int stack_hash_mask;

 /* Array of memory regions that store stack traces. */
 static void *stack_pools[DEPOT_MAX_POOLS];
 /* Currently used pool in stack_pools. */
 static int pool_index;
 /* Offset to the unused space in the currently used pool. */
 static size_t pool_offset;
 /* Lock that protects the variables above. */
 static DEFINE_RAW_SPINLOCK(pool_lock);
 /*
  * Stack depot tries to keep an extra pool allocated even before it runs out
  * of space in the currently used pool.
  * This flag marks that this next extra pool needs to be allocated and
  * initialized. It has the value 0 when either the next pool is not yet
  * initialized or the limit on the number of pools is reached.
  */
 static int next_pool_required = 1;

 static int __init disable_stack_depot(char *str)
 {
 	int ret;

 	ret = kstrtobool(str, &stack_depot_disabled);
 	if (!ret && stack_depot_disabled) {
 		pr_info("disabled\n");
 		stack_table = NULL;
 	}
 	return 0;
 }
 early_param("stack_depot_disable", disable_stack_depot);

 void __init stack_depot_request_early_init(void)
 {
 	/* Too late to request early init now. */
 	WARN_ON(__stack_depot_early_init_passed);

 	__stack_depot_early_init_requested = true;
 }

 /* Allocates a hash table via memblock. Can only be used during early boot. */
 int __init stack_depot_early_init(void)
 {
 	unsigned long entries = 0;

 	/* This function must be called only once, from mm_init(). */
 	if (WARN_ON(__stack_depot_early_init_passed))
 		return 0;
 	__stack_depot_early_init_passed = true;

 	/*
 	 * If KASAN is enabled, use the maximum order: KASAN is frequently used
 	 * in fuzzing scenarios, which leads to a large number of different
 	 * stack traces being stored in stack depot.
 	 */
 	if (kasan_enabled() && !stack_bucket_number_order)
 		stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX;

 	if (!__stack_depot_early_init_requested || stack_depot_disabled)
 		return 0;

 	/*
 	 * If stack_bucket_number_order is not set, leave entries as 0 to rely
 	 * on the automatic calculations performed by alloc_large_system_hash.
 	 */
 	if (stack_bucket_number_order)
 		entries = 1UL << stack_bucket_number_order;
 	pr_info("allocating hash table via alloc_large_system_hash\n");
 	stack_table = alloc_large_system_hash("stackdepot",
 						sizeof(struct stack_record *),
 						entries,
 						STACK_HASH_TABLE_SCALE,
 						HASH_EARLY | HASH_ZERO,
 						NULL,
 						&stack_hash_mask,
 						1UL << STACK_BUCKET_NUMBER_ORDER_MIN,
 						1UL << STACK_BUCKET_NUMBER_ORDER_MAX);
 	if (!stack_table) {
 		pr_err("hash table allocation failed, disabling\n");
 		stack_depot_disabled = true;
 		return -ENOMEM;
 	}

 	return 0;
 }

 /* Allocates a hash table via kvcalloc. Can be used after boot. */
 int stack_depot_init(void)
 {
 	static DEFINE_MUTEX(stack_depot_init_mutex);
 	unsigned long entries;
 	int ret = 0;

 	mutex_lock(&stack_depot_init_mutex);

 	if (stack_depot_disabled || stack_table)
 		goto out_unlock;

 	/*
 	 * Similarly to stack_depot_early_init, use stack_bucket_number_order
 	 * if assigned, and rely on automatic scaling otherwise.
 	 */
 	if (stack_bucket_number_order) {
 		entries = 1UL << stack_bucket_number_order;
 	} else {
 		int scale = STACK_HASH_TABLE_SCALE;

 		entries = nr_free_buffer_pages();
 		entries = roundup_pow_of_two(entries);

 		if (scale > PAGE_SHIFT)
 			entries >>= (scale - PAGE_SHIFT);
 		else
 			entries <<= (PAGE_SHIFT - scale);
 	}

 	if (entries < 1UL << STACK_BUCKET_NUMBER_ORDER_MIN)
 		entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MIN;
 	if (entries > 1UL << STACK_BUCKET_NUMBER_ORDER_MAX)
 		entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MAX;

 	pr_info("allocating hash table of %lu entries via kvcalloc\n", entries);
 	stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL);
 	if (!stack_table) {
 		pr_err("hash table allocation failed, disabling\n");
 		stack_depot_disabled = true;
 		ret = -ENOMEM;
 		goto out_unlock;
 	}
 	stack_hash_mask = entries - 1;

 out_unlock:
 	mutex_unlock(&stack_depot_init_mutex);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(stack_depot_init);

 /* Uses preallocated memory to initialize a new stack depot pool. */
 static void depot_init_pool(void **prealloc)
 {
 	/*
 	 * If the next pool is already initialized or the maximum number of
 	 * pools is reached, do not use the preallocated memory.
 	 * smp_load_acquire() here pairs with smp_store_release() below and
 	 * in depot_alloc_stack().
 	 */
 	if (!smp_load_acquire(&next_pool_required))
 		return;

 	/* Check if the current pool is not yet allocated. */
 	if (stack_pools[pool_index] == NULL) {
 		/* Use the preallocated memory for the current pool. */
 		stack_pools[pool_index] = *prealloc;
 		*prealloc = NULL;
 	} else {
 		/*
 		 * Otherwise, use the preallocated memory for the next pool
 		 * as long as we do not exceed the maximum number of pools.
 		 */
 		if (pool_index + 1 < DEPOT_MAX_POOLS) {
 			stack_pools[pool_index + 1] = *prealloc;
 			*prealloc = NULL;
 		}
 		/*
 		 * At this point, either the next pool is initialized or the
 		 * maximum number of pools is reached. In either case, take
 		 * note that initializing another pool is not required.
 		 * This smp_store_release pairs with smp_load_acquire() above
 		 * and in stack_depot_save().
 		 */
 		smp_store_release(&next_pool_required, 0);
 	}
 }

 /* Allocates a new stack in a stack depot pool. */
 static struct stack_record *
 depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
 {
 	struct stack_record *stack;
 	size_t required_size = struct_size(stack, entries, size);

 	required_size = ALIGN(required_size, 1 << DEPOT_STACK_ALIGN);

 	/* Check if there is not enough space in the current pool. */
 	if (unlikely(pool_offset + required_size > DEPOT_POOL_SIZE)) {
 		/* Bail out if we reached the pool limit. */
 		if (unlikely(pool_index + 1 >= DEPOT_MAX_POOLS)) {
 			WARN_ONCE(1, "Stack depot reached limit capacity");
 			return NULL;
 		}

 		/*
 		 * Move on to the next pool.
 		 * WRITE_ONCE pairs with potential concurrent read in
 		 * stack_depot_fetch().
 		 */
 		WRITE_ONCE(pool_index, pool_index + 1);
 		pool_offset = 0;
 		/*
 		 * If the maximum number of pools is not reached, take note
 		 * that the next pool needs to initialized.
 		 * smp_store_release() here pairs with smp_load_acquire() in
 		 * stack_depot_save() and depot_init_pool().
 		 */
 		if (pool_index + 1 < DEPOT_MAX_POOLS)
 			smp_store_release(&next_pool_required, 1);
 	}

 	/* Assign the preallocated memory to a pool if required. */
 	if (*prealloc)
 		depot_init_pool(prealloc);

 	/* Check if we have a pool to save the stack trace. */
 	if (stack_pools[pool_index] == NULL)
 		return NULL;

 	/* Save the stack trace. */
 	stack = stack_pools[pool_index] + pool_offset;
 	stack->hash = hash;
 	stack->size = size;
 	stack->handle.pool_index = pool_index;
 	stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
 	stack->handle.valid = 1;
 	stack->handle.extra = 0;
 	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
 	pool_offset += required_size;
 	/*
 	 * Let KMSAN know the stored stack record is initialized. This shall
 	 * prevent false positive reports if instrumented code accesses it.
 	 */
 	kmsan_unpoison_memory(stack, required_size);

 	return stack;
 }

 /* Calculates the hash for a stack. */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
 {
 	return jhash2((u32 *)entries,
 		      array_size(size,  sizeof(*entries)) / sizeof(u32),
 		      STACK_HASH_SEED);
 }

 /*
  * Non-instrumented version of memcmp().
  * Does not check the lexicographical order, only the equality.
  */
 static inline
 int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
 			unsigned int n)
 {
 	for ( ; n-- ; u1++, u2++) {
 		if (*u1 != *u2)
 			return 1;
 	}
 	return 0;
 }

 /* Finds a stack in a bucket of the hash table. */
 static inline struct stack_record *find_stack(struct stack_record *bucket,
 					     unsigned long *entries, int size,
 					     u32 hash)
 {
 	struct stack_record *found;

 	for (found = bucket; found; found = found->next) {
 		if (found->hash == hash &&
 		    found->size == size &&
 		    !stackdepot_memcmp(entries, found->entries, size))
 			return found;
 	}
 	return NULL;
 }

 depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 					unsigned int nr_entries,
 					gfp_t alloc_flags, bool can_alloc)
 {
 	struct stack_record *found = NULL, **bucket;
 	union handle_parts retval = { .handle = 0 };
 	struct page *page = NULL;
 	void *prealloc = NULL;
 	unsigned long flags;
 	u32 hash;

 	/*
 	 * If this stack trace is from an interrupt, including anything before
 	 * interrupt entry usually leads to unbounded stack depot growth.
 	 *
 	 * Since use of filter_irq_stacks() is a requirement to ensure stack
 	 * depot can efficiently deduplicate interrupt stacks, always
 	 * filter_irq_stacks() to simplify all callers' use of stack depot.
 	 */
 	nr_entries = filter_irq_stacks(entries, nr_entries);

 	if (unlikely(nr_entries == 0) || stack_depot_disabled)
 		goto fast_exit;

 	hash = hash_stack(entries, nr_entries);
 	bucket = &stack_table[hash & stack_hash_mask];

 	/*
 	 * Fast path: look the stack trace up without locking.
 	 * The smp_load_acquire() here pairs with smp_store_release() to
 	 * |bucket| below.
 	 */
 	found = find_stack(smp_load_acquire(bucket), entries, nr_entries, hash);
 	if (found)
 		goto exit;

 	/*
 	 * Check if another stack pool needs to be initialized. If so, allocate
 	 * the memory now - we won't be able to do that under the lock.
 	 *
 	 * The smp_load_acquire() here pairs with smp_store_release() to
 	 * |next_pool_inited| in depot_alloc_stack() and depot_init_pool().
 	 */
 	if (unlikely(can_alloc && smp_load_acquire(&next_pool_required))) {
 		/*
 		 * Zero out zone modifiers, as we don't have specific zone
 		 * requirements. Keep the flags related to allocation in atomic
 		 * contexts and I/O.
 		 */
 		alloc_flags &= ~GFP_ZONEMASK;
 		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
 		alloc_flags |= __GFP_NOWARN;
 		page = alloc_pages(alloc_flags, DEPOT_POOL_ORDER);
 		if (page)
 			prealloc = page_address(page);
 	}

 	raw_spin_lock_irqsave(&pool_lock, flags);

 	found = find_stack(*bucket, entries, nr_entries, hash);
 	if (!found) {
 		struct stack_record *new =
 			depot_alloc_stack(entries, nr_entries, hash, &prealloc);

 		if (new) {
 			new->next = *bucket;
 			/*
 			 * This smp_store_release() pairs with
 			 * smp_load_acquire() from |bucket| above.
 			 */
 			smp_store_release(bucket, new);
 			found = new;
 		}
 	} else if (prealloc) {
 		/*
 		 * Stack depot already contains this stack trace, but let's
 		 * keep the preallocated memory for the future.
 		 */
 		depot_init_pool(&prealloc);
 	}

 	raw_spin_unlock_irqrestore(&pool_lock, flags);
 exit:
 	if (prealloc) {
 		/* Stack depot didn't use this memory, free it. */
 		free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
 	}
 	if (found)
 		retval.handle = found->handle.handle;
 fast_exit:
 	return retval.handle;
 }
 EXPORT_SYMBOL_GPL(__stack_depot_save);

 depot_stack_handle_t stack_depot_save(unsigned long *entries,
 				      unsigned int nr_entries,
 				      gfp_t alloc_flags)
 {
 	return __stack_depot_save(entries, nr_entries, alloc_flags, true);
 }
 EXPORT_SYMBOL_GPL(stack_depot_save);

 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 			       unsigned long **entries)
 {
 	union handle_parts parts = { .handle = handle };
 	/*
 	 * READ_ONCE pairs with potential concurrent write in
 	 * depot_alloc_stack.
 	 */
 	int pool_index_cached = READ_ONCE(pool_index);
 	void *pool;
 	size_t offset = parts.offset << DEPOT_STACK_ALIGN;
 	struct stack_record *stack;

 	*entries = NULL;
 	/*
 	 * Let KMSAN know *entries is initialized. This shall prevent false
 	 * positive reports if instrumented code accesses it.
 	 */
 	kmsan_unpoison_memory(entries, sizeof(*entries));

 	if (!handle)
 		return 0;

 	if (parts.pool_index > pool_index_cached) {
 		WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
 			parts.pool_index, pool_index_cached, handle);
 		return 0;
 	}
 	pool = stack_pools[parts.pool_index];
 	if (!pool)
 		return 0;
 	stack = pool + offset;

 	*entries = stack->entries;
 	return stack->size;
 }
 EXPORT_SYMBOL_GPL(stack_depot_fetch);

 void stack_depot_print(depot_stack_handle_t stack)
 {
 	unsigned long *entries;
 	unsigned int nr_entries;

 	nr_entries = stack_depot_fetch(stack, &entries);
 	if (nr_entries > 0)
 		stack_trace_print(entries, nr_entries, 0);
 }
 EXPORT_SYMBOL_GPL(stack_depot_print);

 int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
 		       int spaces)
 {
 	unsigned long *entries;
 	unsigned int nr_entries;

 	nr_entries = stack_depot_fetch(handle, &entries);
 	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
 						spaces) : 0;
 }
 EXPORT_SYMBOL_GPL(stack_depot_snprint);

 depot_stack_handle_t __must_check stack_depot_set_extra_bits(
 			depot_stack_handle_t handle, unsigned int extra_bits)
 {
 	union handle_parts parts = { .handle = handle };

 	/* Don't set extra bits on empty handles. */
 	if (!handle)
 		return 0;

 	parts.extra = extra_bits;
 	return parts.handle;
 }
 EXPORT_SYMBOL(stack_depot_set_extra_bits);

 unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
 {
 	union handle_parts parts = { .handle = handle };

 	return parts.extra;
 }
 EXPORT_SYMBOL(stack_depot_get_extra_bits);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Stack depot - a stack trace storage that avoids duplication.
	*
	* Internally, stack depot maintains a hash table of unique stacktraces. The
	* stack traces themselves are stored contiguously one after another in a set
	* of separate page allocations.
	*
	* Author: Alexander Potapenko <glider@google.com>
	* Copyright (C) 2016 Google, Inc.
	*
	* Based on the code by Dmitry Chernenkov.
	*/

	#define pr_fmt(fmt) "stackdepot: " fmt

	#include <linux/gfp.h>
	#include <linux/jhash.h>
	#include <linux/kernel.h>
	#include <linux/kmsan.h>
	#include <linux/mm.h>
	#include <linux/mutex.h>
	#include <linux/percpu.h>
	#include <linux/printk.h>
	#include <linux/slab.h>
	#include <linux/stacktrace.h>
	#include <linux/stackdepot.h>
	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/memblock.h>
	#include <linux/kasan-enabled.h>

	#define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)

	#define DEPOT_VALID_BITS 1
	#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
	#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
	#define DEPOT_STACK_ALIGN 4
	#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
	#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_VALID_BITS - \
	DEPOT_OFFSET_BITS - STACK_DEPOT_EXTRA_BITS)
	#define DEPOT_POOLS_CAP 8192
	#define DEPOT_MAX_POOLS \
	(((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
	(1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)

	/* Compact structure that stores a reference to a stack. */
	union handle_parts {
	depot_stack_handle_t handle;
	struct {
	u32 pool_index : DEPOT_POOL_INDEX_BITS;
	u32 offset : DEPOT_OFFSET_BITS;
	u32 valid : DEPOT_VALID_BITS;
	u32 extra : STACK_DEPOT_EXTRA_BITS;
	};
	};

	struct stack_record {
	struct stack_record next; / Link in the hash table */
	u32 hash; /* Hash in the hash table */
	u32 size; /* Number of stored frames */
	union handle_parts handle;
	unsigned long entries[]; /* Variable-sized array of frames */
	};

	static bool stack_depot_disabled;
	static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
	static bool __stack_depot_early_init_passed __initdata;

	/* Use one hash table bucket per 16 KB of memory. */
	#define STACK_HASH_TABLE_SCALE 14
	/* Limit the number of buckets between 4K and 1M. */
	#define STACK_BUCKET_NUMBER_ORDER_MIN 12
	#define STACK_BUCKET_NUMBER_ORDER_MAX 20
	/* Initial seed for jhash2. */
	#define STACK_HASH_SEED 0x9747b28c

	/* Hash table of pointers to stored stack traces. */
	static struct stack_record **stack_table;
	/* Fixed order of the number of table buckets. Used when KASAN is enabled. */
	static unsigned int stack_bucket_number_order;
	/* Hash mask for indexing the table. */
	static unsigned int stack_hash_mask;

	/* Array of memory regions that store stack traces. */
	static void *stack_pools[DEPOT_MAX_POOLS];
	/* Currently used pool in stack_pools. */
	static int pool_index;
	/* Offset to the unused space in the currently used pool. */
	static size_t pool_offset;
	/* Lock that protects the variables above. */
	static DEFINE_RAW_SPINLOCK(pool_lock);
	/*
	* Stack depot tries to keep an extra pool allocated even before it runs out
	* of space in the currently used pool.
	* This flag marks that this next extra pool needs to be allocated and
	* initialized. It has the value 0 when either the next pool is not yet
	* initialized or the limit on the number of pools is reached.
	*/
	static int next_pool_required = 1;

	static int __init disable_stack_depot(char *str)
	{
	int ret;

	ret = kstrtobool(str, &stack_depot_disabled);
	if (!ret && stack_depot_disabled) {
	pr_info("disabled\n");
	stack_table = NULL;
	}
	return 0;
	}
	early_param("stack_depot_disable", disable_stack_depot);

	void __init stack_depot_request_early_init(void)
	{
	/* Too late to request early init now. */
	WARN_ON(__stack_depot_early_init_passed);

	__stack_depot_early_init_requested = true;
	}

	/* Allocates a hash table via memblock. Can only be used during early boot. */
	int __init stack_depot_early_init(void)
	{
	unsigned long entries = 0;

	/* This function must be called only once, from mm_init(). */
	if (WARN_ON(__stack_depot_early_init_passed))
	return 0;
	__stack_depot_early_init_passed = true;

	/*
	* If KASAN is enabled, use the maximum order: KASAN is frequently used
	* in fuzzing scenarios, which leads to a large number of different
	* stack traces being stored in stack depot.
	*/
	if (kasan_enabled() && !stack_bucket_number_order)
	stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX;

	if (!__stack_depot_early_init_requested \|\| stack_depot_disabled)
	return 0;

	/*
	* If stack_bucket_number_order is not set, leave entries as 0 to rely
	* on the automatic calculations performed by alloc_large_system_hash.
	*/
	if (stack_bucket_number_order)
	entries = 1UL << stack_bucket_number_order;
	pr_info("allocating hash table via alloc_large_system_hash\n");
	stack_table = alloc_large_system_hash("stackdepot",
	sizeof(struct stack_record *),
	entries,
	STACK_HASH_TABLE_SCALE,
	HASH_EARLY \| HASH_ZERO,
	NULL,
	&stack_hash_mask,
	1UL << STACK_BUCKET_NUMBER_ORDER_MIN,
	1UL << STACK_BUCKET_NUMBER_ORDER_MAX);
	if (!stack_table) {
	pr_err("hash table allocation failed, disabling\n");
	stack_depot_disabled = true;
	return -ENOMEM;
	}

	return 0;
	}

	/* Allocates a hash table via kvcalloc. Can be used after boot. */
	int stack_depot_init(void)
	{
	static DEFINE_MUTEX(stack_depot_init_mutex);
	unsigned long entries;
	int ret = 0;

	mutex_lock(&stack_depot_init_mutex);

	if (stack_depot_disabled \|\| stack_table)
	goto out_unlock;

	/*
	* Similarly to stack_depot_early_init, use stack_bucket_number_order
	* if assigned, and rely on automatic scaling otherwise.
	*/
	if (stack_bucket_number_order) {
	entries = 1UL << stack_bucket_number_order;
	} else {
	int scale = STACK_HASH_TABLE_SCALE;

	entries = nr_free_buffer_pages();
	entries = roundup_pow_of_two(entries);

	if (scale > PAGE_SHIFT)
	entries >>= (scale - PAGE_SHIFT);
	else
	entries <<= (PAGE_SHIFT - scale);
	}

	if (entries < 1UL << STACK_BUCKET_NUMBER_ORDER_MIN)
	entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MIN;
	if (entries > 1UL << STACK_BUCKET_NUMBER_ORDER_MAX)
	entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MAX;

	pr_info("allocating hash table of %lu entries via kvcalloc\n", entries);
	stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL);
	if (!stack_table) {
	pr_err("hash table allocation failed, disabling\n");
	stack_depot_disabled = true;
	ret = -ENOMEM;
	goto out_unlock;
	}
	stack_hash_mask = entries - 1;

	out_unlock:
	mutex_unlock(&stack_depot_init_mutex);

	return ret;
	}
	EXPORT_SYMBOL_GPL(stack_depot_init);

	/* Uses preallocated memory to initialize a new stack depot pool. */
	static void depot_init_pool(void **prealloc)
	{
	/*
	* If the next pool is already initialized or the maximum number of
	* pools is reached, do not use the preallocated memory.
	* smp_load_acquire() here pairs with smp_store_release() below and
	* in depot_alloc_stack().
	*/
	if (!smp_load_acquire(&next_pool_required))
	return;

	/* Check if the current pool is not yet allocated. */
	if (stack_pools[pool_index] == NULL) {
	/* Use the preallocated memory for the current pool. */
	stack_pools[pool_index] = *prealloc;
	*prealloc = NULL;
	} else {
	/*
	* Otherwise, use the preallocated memory for the next pool
	* as long as we do not exceed the maximum number of pools.
	*/
	if (pool_index + 1 < DEPOT_MAX_POOLS) {
	stack_pools[pool_index + 1] = *prealloc;
	*prealloc = NULL;
	}
	/*
	* At this point, either the next pool is initialized or the
	* maximum number of pools is reached. In either case, take
	* note that initializing another pool is not required.
	* This smp_store_release pairs with smp_load_acquire() above
	* and in stack_depot_save().
	*/
	smp_store_release(&next_pool_required, 0);
	}
	}

	/* Allocates a new stack in a stack depot pool. */
	static struct stack_record *
	depot_alloc_stack(unsigned long entries, int size, u32 hash, void *prealloc)
	{
	struct stack_record *stack;
	size_t required_size = struct_size(stack, entries, size);

	required_size = ALIGN(required_size, 1 << DEPOT_STACK_ALIGN);

	/* Check if there is not enough space in the current pool. */
	if (unlikely(pool_offset + required_size > DEPOT_POOL_SIZE)) {
	/* Bail out if we reached the pool limit. */
	if (unlikely(pool_index + 1 >= DEPOT_MAX_POOLS)) {
	WARN_ONCE(1, "Stack depot reached limit capacity");
	return NULL;
	}

	/*
	* Move on to the next pool.
	* WRITE_ONCE pairs with potential concurrent read in
	* stack_depot_fetch().
	*/
	WRITE_ONCE(pool_index, pool_index + 1);
	pool_offset = 0;
	/*
	* If the maximum number of pools is not reached, take note
	* that the next pool needs to initialized.
	* smp_store_release() here pairs with smp_load_acquire() in
	* stack_depot_save() and depot_init_pool().
	*/
	if (pool_index + 1 < DEPOT_MAX_POOLS)
	smp_store_release(&next_pool_required, 1);
	}

	/* Assign the preallocated memory to a pool if required. */
	if (*prealloc)
	depot_init_pool(prealloc);

	/* Check if we have a pool to save the stack trace. */
	if (stack_pools[pool_index] == NULL)
	return NULL;

	/* Save the stack trace. */
	stack = stack_pools[pool_index] + pool_offset;
	stack->hash = hash;
	stack->size = size;
	stack->handle.pool_index = pool_index;
	stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
	stack->handle.valid = 1;
	stack->handle.extra = 0;
	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
	pool_offset += required_size;
	/*
	* Let KMSAN know the stored stack record is initialized. This shall
	* prevent false positive reports if instrumented code accesses it.
	*/
	kmsan_unpoison_memory(stack, required_size);

	return stack;
	}

	/* Calculates the hash for a stack. */
	static inline u32 hash_stack(unsigned long *entries, unsigned int size)
	{
	return jhash2((u32 *)entries,
	array_size(size, sizeof(*entries)) / sizeof(u32),
	STACK_HASH_SEED);
	}

	/*
	* Non-instrumented version of memcmp().
	* Does not check the lexicographical order, only the equality.
	*/
	static inline
	int stackdepot_memcmp(const unsigned long u1, const unsigned long u2,
	unsigned int n)
	{
	for ( ; n-- ; u1++, u2++) {
	if (u1 != u2)
	return 1;
	}
	return 0;
	}

	/* Finds a stack in a bucket of the hash table. */
	static inline struct stack_record find_stack(struct stack_record bucket,
	unsigned long *entries, int size,
	u32 hash)
	{
	struct stack_record *found;

	for (found = bucket; found; found = found->next) {
	if (found->hash == hash &&
	found->size == size &&
	!stackdepot_memcmp(entries, found->entries, size))
	return found;
	}
	return NULL;
	}

	depot_stack_handle_t __stack_depot_save(unsigned long *entries,
	unsigned int nr_entries,
	gfp_t alloc_flags, bool can_alloc)
	{
	struct stack_record found = NULL, *bucket;
	union handle_parts retval = { .handle = 0 };
	struct page *page = NULL;
	void *prealloc = NULL;
	unsigned long flags;
	u32 hash;

	/*
	* If this stack trace is from an interrupt, including anything before
	* interrupt entry usually leads to unbounded stack depot growth.
	*
	* Since use of filter_irq_stacks() is a requirement to ensure stack
	* depot can efficiently deduplicate interrupt stacks, always
	* filter_irq_stacks() to simplify all callers' use of stack depot.
	*/
	nr_entries = filter_irq_stacks(entries, nr_entries);

	if (unlikely(nr_entries == 0) \|\| stack_depot_disabled)
	goto fast_exit;

	hash = hash_stack(entries, nr_entries);
	bucket = &stack_table[hash & stack_hash_mask];

	/*
	* Fast path: look the stack trace up without locking.
	* The smp_load_acquire() here pairs with smp_store_release() to
	* \|bucket\| below.
	*/
	found = find_stack(smp_load_acquire(bucket), entries, nr_entries, hash);
	if (found)
	goto exit;

	/*
	* Check if another stack pool needs to be initialized. If so, allocate
	* the memory now - we won't be able to do that under the lock.
	*
	* The smp_load_acquire() here pairs with smp_store_release() to
	* \|next_pool_inited\| in depot_alloc_stack() and depot_init_pool().
	*/
	if (unlikely(can_alloc && smp_load_acquire(&next_pool_required))) {
	/*
	* Zero out zone modifiers, as we don't have specific zone
	* requirements. Keep the flags related to allocation in atomic
	* contexts and I/O.
	*/
	alloc_flags &= ~GFP_ZONEMASK;
	alloc_flags &= (GFP_ATOMIC \| GFP_KERNEL);
	alloc_flags \|= __GFP_NOWARN;
	page = alloc_pages(alloc_flags, DEPOT_POOL_ORDER);
	if (page)
	prealloc = page_address(page);
	}

	raw_spin_lock_irqsave(&pool_lock, flags);

	found = find_stack(*bucket, entries, nr_entries, hash);
	if (!found) {
	struct stack_record *new =
	depot_alloc_stack(entries, nr_entries, hash, &prealloc);

	if (new) {
	new->next = *bucket;
	/*
	* This smp_store_release() pairs with
	* smp_load_acquire() from \|bucket\| above.
	*/
	smp_store_release(bucket, new);
	found = new;
	}
	} else if (prealloc) {
	/*
	* Stack depot already contains this stack trace, but let's
	* keep the preallocated memory for the future.
	*/
	depot_init_pool(&prealloc);
	}

	raw_spin_unlock_irqrestore(&pool_lock, flags);
	exit:
	if (prealloc) {
	/* Stack depot didn't use this memory, free it. */
	free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
	}
	if (found)
	retval.handle = found->handle.handle;
	fast_exit:
	return retval.handle;
	}
	EXPORT_SYMBOL_GPL(__stack_depot_save);

	depot_stack_handle_t stack_depot_save(unsigned long *entries,
	unsigned int nr_entries,
	gfp_t alloc_flags)
	{
	return __stack_depot_save(entries, nr_entries, alloc_flags, true);
	}
	EXPORT_SYMBOL_GPL(stack_depot_save);

	unsigned int stack_depot_fetch(depot_stack_handle_t handle,
	unsigned long **entries)
	{
	union handle_parts parts = { .handle = handle };
	/*
	* READ_ONCE pairs with potential concurrent write in
	* depot_alloc_stack.
	*/
	int pool_index_cached = READ_ONCE(pool_index);
	void *pool;
	size_t offset = parts.offset << DEPOT_STACK_ALIGN;
	struct stack_record *stack;

	*entries = NULL;
	/*
	* Let KMSAN know *entries is initialized. This shall prevent false
	* positive reports if instrumented code accesses it.
	*/
	kmsan_unpoison_memory(entries, sizeof(*entries));

	if (!handle)
	return 0;

	if (parts.pool_index > pool_index_cached) {
	WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
	parts.pool_index, pool_index_cached, handle);
	return 0;
	}
	pool = stack_pools[parts.pool_index];
	if (!pool)
	return 0;
	stack = pool + offset;

	*entries = stack->entries;
	return stack->size;
	}
	EXPORT_SYMBOL_GPL(stack_depot_fetch);

	void stack_depot_print(depot_stack_handle_t stack)
	{
	unsigned long *entries;
	unsigned int nr_entries;

	nr_entries = stack_depot_fetch(stack, &entries);
	if (nr_entries > 0)
	stack_trace_print(entries, nr_entries, 0);
	}
	EXPORT_SYMBOL_GPL(stack_depot_print);

	int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
	int spaces)
	{
	unsigned long *entries;
	unsigned int nr_entries;

	nr_entries = stack_depot_fetch(handle, &entries);
	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
	spaces) : 0;
	}
	EXPORT_SYMBOL_GPL(stack_depot_snprint);

	depot_stack_handle_t __must_check stack_depot_set_extra_bits(
	depot_stack_handle_t handle, unsigned int extra_bits)
	{
	union handle_parts parts = { .handle = handle };

	/* Don't set extra bits on empty handles. */
	if (!handle)
	return 0;

	parts.extra = extra_bits;
	return parts.handle;
	}
	EXPORT_SYMBOL(stack_depot_set_extra_bits);

	unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
	{
	union handle_parts parts = { .handle = handle };

	return parts.extra;
	}
	EXPORT_SYMBOL(stack_depot_get_extra_bits);