Merge tag 'bcachefs-2024-04-22' of https://evilpiepirate.org/git/bcachefs

[thirdparty/kernel/linux.git] / lib / stackdepot.c

// 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/debugfs.h>
#include <linux/gfp.h>
#include <linux/jhash.h>
#include <linux/kernel.h>
#include <linux/kmsan.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/poison.h>
#include <linux/printk.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/refcount.h>
#include <linux/slab.h>
#include <linux/spinlock.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_POOLS_CAP 8192
/* The pool_index is offset by 1 so the first record does not have a 0 handle. */
#define DEPOT_MAX_POOLS \
        (((1LL << (DEPOT_POOL_INDEX_BITS)) - 1 < DEPOT_POOLS_CAP) ? \
         (1LL << (DEPOT_POOL_INDEX_BITS)) - 1 : DEPOT_POOLS_CAP)

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 stored stack records. */
static struct list_head *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 records. */
static void *stack_pools[DEPOT_MAX_POOLS];
/* Newly allocated pool that is not yet added to stack_pools. */
static void *new_pool;
/* Number of pools in stack_pools. */
static int pools_num;
/* Offset to the unused space in the currently used pool. */
static size_t pool_offset = DEPOT_POOL_SIZE;
/* Freelist of stack records within stack_pools. */
static LIST_HEAD(free_stacks);
/* The lock must be held when performing pool or freelist modifications. */
static DEFINE_RAW_SPINLOCK(pool_lock);

/* Statistics counters for debugfs. */
enum depot_counter_id {
        DEPOT_COUNTER_REFD_ALLOCS,
        DEPOT_COUNTER_REFD_FREES,
        DEPOT_COUNTER_REFD_INUSE,
        DEPOT_COUNTER_FREELIST_SIZE,
        DEPOT_COUNTER_PERSIST_COUNT,
        DEPOT_COUNTER_PERSIST_BYTES,
        DEPOT_COUNTER_COUNT,
};
static long counters[DEPOT_COUNTER_COUNT];
static const char *const counter_names[] = {
        [DEPOT_COUNTER_REFD_ALLOCS]     = "refcounted_allocations",
        [DEPOT_COUNTER_REFD_FREES]      = "refcounted_frees",
        [DEPOT_COUNTER_REFD_INUSE]      = "refcounted_in_use",
        [DEPOT_COUNTER_FREELIST_SIZE]   = "freelist_size",
        [DEPOT_COUNTER_PERSIST_COUNT]   = "persistent_count",
        [DEPOT_COUNTER_PERSIST_BYTES]   = "persistent_bytes",
};
static_assert(ARRAY_SIZE(counter_names) == DEPOT_COUNTER_COUNT);

static int __init disable_stack_depot(char *str)
{
        return kstrtobool(str, &stack_depot_disabled);
}
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;
}

/* Initialize list_head's within the hash table. */
static void init_stack_table(unsigned long entries)
{
        unsigned long i;

        for (i = 0; i < entries; i++)
                INIT_LIST_HEAD(&stack_table[i]);
}

/* 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;

        /*
         * Print disabled message even if early init has not been requested:
         * stack_depot_init() will not print one.
         */
        if (stack_depot_disabled) {
                pr_info("disabled\n");
                return 0;
        }

        /*
         * 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;

        /*
         * Check if early init has been requested after setting
         * stack_bucket_number_order: stack_depot_init() uses its value.
         */
        if (!__stack_depot_early_init_requested)
                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 list_head),
                                                entries,
                                                STACK_HASH_TABLE_SCALE,
                                                HASH_EARLY,
                                                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;
        }
        if (!entries) {
                /*
                 * Obtain the number of entries that was calculated by
                 * alloc_large_system_hash().
                 */
                entries = stack_hash_mask + 1;
        }
        init_stack_table(entries);

        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 list_head), 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;
        init_stack_table(entries);

out_unlock:
        mutex_unlock(&stack_depot_init_mutex);

        return ret;
}
EXPORT_SYMBOL_GPL(stack_depot_init);

/*
 * Initializes new stack pool, and updates the list of pools.
 */
static bool depot_init_pool(void **prealloc)
{
        lockdep_assert_held(&pool_lock);

        if (unlikely(pools_num >= DEPOT_MAX_POOLS)) {
                /* Bail out if we reached the pool limit. */
                WARN_ON_ONCE(pools_num > DEPOT_MAX_POOLS); /* should never happen */
                WARN_ON_ONCE(!new_pool); /* to avoid unnecessary pre-allocation */
                WARN_ONCE(1, "Stack depot reached limit capacity");
                return false;
        }

        if (!new_pool && *prealloc) {
                /* We have preallocated memory, use it. */
                WRITE_ONCE(new_pool, *prealloc);
                *prealloc = NULL;
        }

        if (!new_pool)
                return false; /* new_pool and *prealloc are NULL */

        /* Save reference to the pool to be used by depot_fetch_stack(). */
        stack_pools[pools_num] = new_pool;

        /*
         * Stack depot tries to keep an extra pool allocated even before it runs
         * out of space in the currently used pool.
         *
         * To indicate that a new preallocation is needed new_pool is reset to
         * NULL; do not reset to NULL if we have reached the maximum number of
         * pools.
         */
        if (pools_num < DEPOT_MAX_POOLS)
                WRITE_ONCE(new_pool, NULL);
        else
                WRITE_ONCE(new_pool, STACK_DEPOT_POISON);

        /* Pairs with concurrent READ_ONCE() in depot_fetch_stack(). */
        WRITE_ONCE(pools_num, pools_num + 1);
        ASSERT_EXCLUSIVE_WRITER(pools_num);

        pool_offset = 0;

        return true;
}

/* Keeps the preallocated memory to be used for a new stack depot pool. */
static void depot_keep_new_pool(void **prealloc)
{
        lockdep_assert_held(&pool_lock);

        /*
         * If a new pool is already saved or the maximum number of
         * pools is reached, do not use the preallocated memory.
         */
        if (new_pool)
                return;

        WRITE_ONCE(new_pool, *prealloc);
        *prealloc = NULL;
}

/*
 * Try to initialize a new stack record from the current pool, a cached pool, or
 * the current pre-allocation.
 */
static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
{
        struct stack_record *stack;
        void *current_pool;
        u32 pool_index;

        lockdep_assert_held(&pool_lock);

        if (pool_offset + size > DEPOT_POOL_SIZE) {
                if (!depot_init_pool(prealloc))
                        return NULL;
        }

        if (WARN_ON_ONCE(pools_num < 1))
                return NULL;
        pool_index = pools_num - 1;
        current_pool = stack_pools[pool_index];
        if (WARN_ON_ONCE(!current_pool))
                return NULL;

        stack = current_pool + pool_offset;

        /* Pre-initialize handle once. */
        stack->handle.pool_index_plus_1 = pool_index + 1;
        stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
        stack->handle.extra = 0;
        INIT_LIST_HEAD(&stack->hash_list);

        pool_offset += size;

        return stack;
}

/* Try to find next free usable entry from the freelist. */
static struct stack_record *depot_pop_free(void)
{
        struct stack_record *stack;

        lockdep_assert_held(&pool_lock);

        if (list_empty(&free_stacks))
                return NULL;

        /*
         * We maintain the invariant that the elements in front are least
         * recently used, and are therefore more likely to be associated with an
         * RCU grace period in the past. Consequently it is sufficient to only
         * check the first entry.
         */
        stack = list_first_entry(&free_stacks, struct stack_record, free_list);
        if (!poll_state_synchronize_rcu(stack->rcu_state))
                return NULL;

        list_del(&stack->free_list);
        counters[DEPOT_COUNTER_FREELIST_SIZE]--;

        return stack;
}

static inline size_t depot_stack_record_size(struct stack_record *s, unsigned int nr_entries)
{
        const size_t used = flex_array_size(s, entries, nr_entries);
        const size_t unused = sizeof(s->entries) - used;

        WARN_ON_ONCE(sizeof(s->entries) < used);

        return ALIGN(sizeof(struct stack_record) - unused, 1 << DEPOT_STACK_ALIGN);
}

/* Allocates a new stack in a stack depot pool. */
static struct stack_record *
depot_alloc_stack(unsigned long *entries, unsigned int nr_entries, u32 hash, depot_flags_t flags, void **prealloc)
{
        struct stack_record *stack = NULL;
        size_t record_size;

        lockdep_assert_held(&pool_lock);

        /* This should already be checked by public API entry points. */
        if (WARN_ON_ONCE(!nr_entries))
                return NULL;

        /* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */
        if (nr_entries > CONFIG_STACKDEPOT_MAX_FRAMES)
                nr_entries = CONFIG_STACKDEPOT_MAX_FRAMES;

        if (flags & STACK_DEPOT_FLAG_GET) {
                /*
                 * Evictable entries have to allocate the max. size so they may
                 * safely be re-used by differently sized allocations.
                 */
                record_size = depot_stack_record_size(stack, CONFIG_STACKDEPOT_MAX_FRAMES);
                stack = depot_pop_free();
        } else {
                record_size = depot_stack_record_size(stack, nr_entries);
        }

        if (!stack) {
                stack = depot_pop_free_pool(prealloc, record_size);
                if (!stack)
                        return NULL;
        }

        /* Save the stack trace. */
        stack->hash = hash;
        stack->size = nr_entries;
        /* stack->handle is already filled in by depot_pop_free_pool(). */
        memcpy(stack->entries, entries, flex_array_size(stack, entries, nr_entries));

        if (flags & STACK_DEPOT_FLAG_GET) {
                refcount_set(&stack->count, 1);
                counters[DEPOT_COUNTER_REFD_ALLOCS]++;
                counters[DEPOT_COUNTER_REFD_INUSE]++;
        } else {
                /* Warn on attempts to switch to refcounting this entry. */
                refcount_set(&stack->count, REFCOUNT_SATURATED);
                counters[DEPOT_COUNTER_PERSIST_COUNT]++;
                counters[DEPOT_COUNTER_PERSIST_BYTES] += record_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, record_size);

        return stack;
}

static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
{
        const int pools_num_cached = READ_ONCE(pools_num);
        union handle_parts parts = { .handle = handle };
        void *pool;
        u32 pool_index = parts.pool_index_plus_1 - 1;
        size_t offset = parts.offset << DEPOT_STACK_ALIGN;
        struct stack_record *stack;

        lockdep_assert_not_held(&pool_lock);

        if (pool_index >= pools_num_cached) {
                WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
                     pool_index, pools_num_cached, handle);
                return NULL;
        }

        pool = stack_pools[pool_index];
        if (WARN_ON(!pool))
                return NULL;

        stack = pool + offset;
        if (WARN_ON(!refcount_read(&stack->count)))
                return NULL;

        return stack;
}

/* Links stack into the freelist. */
static void depot_free_stack(struct stack_record *stack)
{
        unsigned long flags;

        lockdep_assert_not_held(&pool_lock);

        raw_spin_lock_irqsave(&pool_lock, flags);
        printk_deferred_enter();

        /*
         * Remove the entry from the hash list. Concurrent list traversal may
         * still observe the entry, but since the refcount is zero, this entry
         * will no longer be considered as valid.
         */
        list_del_rcu(&stack->hash_list);

        /*
         * Due to being used from constrained contexts such as the allocators,
         * NMI, or even RCU itself, stack depot cannot rely on primitives that
         * would sleep (such as synchronize_rcu()) or recursively call into
         * stack depot again (such as call_rcu()).
         *
         * Instead, get an RCU cookie, so that we can ensure this entry isn't
         * moved onto another list until the next grace period, and concurrent
         * RCU list traversal remains safe.
         */
        stack->rcu_state = get_state_synchronize_rcu();

        /*
         * Add the entry to the freelist tail, so that older entries are
         * considered first - their RCU cookie is more likely to no longer be
         * associated with the current grace period.
         */
        list_add_tail(&stack->free_list, &free_stacks);

        counters[DEPOT_COUNTER_FREELIST_SIZE]++;
        counters[DEPOT_COUNTER_REFD_FREES]++;
        counters[DEPOT_COUNTER_REFD_INUSE]--;

        printk_deferred_exit();
        raw_spin_unlock_irqrestore(&pool_lock, flags);
}

/* 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 list_head *bucket,
                                              unsigned long *entries, int size,
                                              u32 hash, depot_flags_t flags)
{
        struct stack_record *stack, *ret = NULL;

        /*
         * Stack depot may be used from instrumentation that instruments RCU or
         * tracing itself; use variant that does not call into RCU and cannot be
         * traced.
         *
         * Note: Such use cases must take care when using refcounting to evict
         * unused entries, because the stack record free-then-reuse code paths
         * do call into RCU.
         */
        rcu_read_lock_sched_notrace();

        list_for_each_entry_rcu(stack, bucket, hash_list) {
                if (stack->hash != hash || stack->size != size)
                        continue;

                /*
                 * This may race with depot_free_stack() accessing the freelist
                 * management state unioned with @entries. The refcount is zero
                 * in that case and the below refcount_inc_not_zero() will fail.
                 */
                if (data_race(stackdepot_memcmp(entries, stack->entries, size)))
                        continue;

                /*
                 * Try to increment refcount. If this succeeds, the stack record
                 * is valid and has not yet been freed.
                 *
                 * If STACK_DEPOT_FLAG_GET is not used, it is undefined behavior
                 * to then call stack_depot_put() later, and we can assume that
                 * a stack record is never placed back on the freelist.
                 */
                if ((flags & STACK_DEPOT_FLAG_GET) && !refcount_inc_not_zero(&stack->count))
                        continue;

                ret = stack;
                break;
        }

        rcu_read_unlock_sched_notrace();

        return ret;
}

depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
                                            unsigned int nr_entries,
                                            gfp_t alloc_flags,
                                            depot_flags_t depot_flags)
{
        struct list_head *bucket;
        struct stack_record *found = NULL;
        depot_stack_handle_t handle = 0;
        struct page *page = NULL;
        void *prealloc = NULL;
        bool can_alloc = depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC;
        unsigned long flags;
        u32 hash;

        if (WARN_ON(depot_flags & ~STACK_DEPOT_FLAGS_MASK))
                return 0;

        /*
         * 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)
                return 0;

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

        /* Fast path: look the stack trace up without locking. */
        found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
        if (found)
                goto exit;

        /*
         * Allocate memory for a new pool if required now:
         * we won't be able to do that under the lock.
         */
        if (unlikely(can_alloc && !READ_ONCE(new_pool))) {
                /*
                 * 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);
        printk_deferred_enter();

        /* Try to find again, to avoid concurrently inserting duplicates. */
        found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
        if (!found) {
                struct stack_record *new =
                        depot_alloc_stack(entries, nr_entries, hash, depot_flags, &prealloc);

                if (new) {
                        /*
                         * This releases the stack record into the bucket and
                         * makes it visible to readers in find_stack().
                         */
                        list_add_rcu(&new->hash_list, bucket);
                        found = new;
                }
        }

        if (prealloc) {
                /*
                 * Either stack depot already contains this stack trace, or
                 * depot_alloc_stack() did not consume the preallocated memory.
                 * Try to keep the preallocated memory for future.
                 */
                depot_keep_new_pool(&prealloc);
        }

        printk_deferred_exit();
        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)
                handle = found->handle.handle;
        return handle;
}
EXPORT_SYMBOL_GPL(stack_depot_save_flags);

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

struct stack_record *__stack_depot_get_stack_record(depot_stack_handle_t handle)
{
        if (!handle)
                return NULL;

        return depot_fetch_stack(handle);
}

unsigned int stack_depot_fetch(depot_stack_handle_t handle,
                               unsigned long **entries)
{
        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 || stack_depot_disabled)
                return 0;

        stack = depot_fetch_stack(handle);
        /*
         * Should never be NULL, otherwise this is a use-after-put (or just a
         * corrupt handle).
         */
        if (WARN(!stack, "corrupt handle or use after stack_depot_put()"))
                return 0;

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

void stack_depot_put(depot_stack_handle_t handle)
{
        struct stack_record *stack;

        if (!handle || stack_depot_disabled)
                return;

        stack = depot_fetch_stack(handle);
        /*
         * Should always be able to find the stack record, otherwise this is an
         * unbalanced put attempt (or corrupt handle).
         */
        if (WARN(!stack, "corrupt handle or unbalanced stack_depot_put()"))
                return;

        if (refcount_dec_and_test(&stack->count))
                depot_free_stack(stack);
}
EXPORT_SYMBOL_GPL(stack_depot_put);

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);

static int stats_show(struct seq_file *seq, void *v)
{
        /*
         * data race ok: These are just statistics counters, and approximate
         * statistics are ok for debugging.
         */
        seq_printf(seq, "pools: %d\n", data_race(pools_num));
        for (int i = 0; i < DEPOT_COUNTER_COUNT; i++)
                seq_printf(seq, "%s: %ld\n", counter_names[i], data_race(counters[i]));

        return 0;
}
DEFINE_SHOW_ATTRIBUTE(stats);

static int depot_debugfs_init(void)
{
        struct dentry *dir;

        if (stack_depot_disabled)
                return 0;

        dir = debugfs_create_dir("stackdepot", NULL);
        debugfs_create_file("stats", 0444, dir, NULL, &stats_fops);
        return 0;
}
late_initcall(depot_debugfs_init);