linux-stable/lib/stackdepot.c
Marco Elver 4434a56ec2 stackdepot: make fast paths lock-less again
With the introduction of the pool_rwlock (reader-writer lock), several
fast paths end up taking the pool_rwlock as readers.  Furthermore,
stack_depot_put() unconditionally takes the pool_rwlock as a writer.

Despite allowing readers to make forward-progress concurrently,
reader-writer locks have inherent cache contention issues, which does not
scale well on systems with large CPU counts.

Rework the synchronization story of stack depot to again avoid taking any
locks in the fast paths.  This is done by relying on RCU-protected list
traversal, and the NMI-safe subset of RCU to delay reuse of freed stack
records.  See code comments for more details.

Along with the performance issues, this also fixes incorrect nesting of
rwlock within a raw_spinlock, given that stack depot should still be
usable from anywhere:

 | [ BUG: Invalid wait context ]
 | -----------------------------
 | swapper/0/1 is trying to lock:
 | ffffffff89869be8 (pool_rwlock){..--}-{3:3}, at: stack_depot_save_flags
 | other info that might help us debug this:
 | context-{5:5}
 | 2 locks held by swapper/0/1:
 |  #0: ffffffff89632440 (rcu_read_lock){....}-{1:3}, at: __queue_work
 |  #1: ffff888100092018 (&pool->lock){-.-.}-{2:2}, at: __queue_work  <-- raw_spin_lock

Stack depot usage stats are similar to the previous version after a KASAN
kernel boot:

 $ cat /sys/kernel/debug/stackdepot/stats
 pools: 838
 allocations: 29865
 frees: 6604
 in_use: 23261
 freelist_size: 1879

The number of pools is the same as previously.  The freelist size is
minimally larger, but this may also be due to variance across system
boots.  This shows that even though we do not eagerly wait for the next
RCU grace period (such as with synchronize_rcu() or call_rcu()) after
freeing a stack record - requiring depot_pop_free() to "poll" if an entry
may be used - new allocations are very likely to happen in later RCU grace
periods.

Link: https://lkml.kernel.org/r/20240118110216.2539519-2-elver@google.com
Fixes: 108be8def4 ("lib/stackdepot: allow users to evict stack traces")
Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-01-25 23:52:21 -08:00

845 lines
24 KiB
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/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_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
#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_OFFSET_BITS - \
STACK_DEPOT_EXTRA_BITS)
#if IS_ENABLED(CONFIG_KMSAN) && CONFIG_STACKDEPOT_MAX_FRAMES >= 32
/*
* KMSAN is frequently used in fuzzing scenarios and thus saves a lot of stack
* traces. As KMSAN does not support evicting stack traces from the stack
* depot, the stack depot capacity might be reached quickly with large stack
* records. Adjust the maximum number of stack depot pools for this case.
*/
#define DEPOT_POOLS_CAP (8192 * (CONFIG_STACKDEPOT_MAX_FRAMES / 16))
#else
#define DEPOT_POOLS_CAP 8192
#endif
#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 extra : STACK_DEPOT_EXTRA_BITS;
};
};
struct stack_record {
struct list_head hash_list; /* Links in the hash table */
u32 hash; /* Hash in hash table */
u32 size; /* Number of stored frames */
union handle_parts handle; /* Constant after initialization */
refcount_t count;
union {
unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES]; /* Frames */
struct {
/*
* An important invariant of the implementation is to
* only place a stack record onto the freelist iff its
* refcount is zero. Because stack records with a zero
* refcount are never considered as valid, it is safe to
* union @entries and freelist management state below.
* Conversely, as soon as an entry is off the freelist
* and its refcount becomes non-zero, the below must not
* be accessed until being placed back on the freelist.
*/
struct list_head free_list; /* Links in the freelist */
unsigned long rcu_state; /* RCU cookie */
};
};
};
#define DEPOT_STACK_RECORD_SIZE \
ALIGN(sizeof(struct stack_record), 1 << DEPOT_STACK_ALIGN)
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;
/* Freelist of stack records within stack_pools. */
static LIST_HEAD(free_stacks);
/*
* Stack depot tries to keep an extra pool allocated even before it runs out
* of space in the currently used pool. This flag marks whether this extra pool
* needs to be allocated. It has the value 0 when either an extra pool is not
* yet allocated or if the limit on the number of pools is reached.
*/
static bool new_pool_required = true;
/* 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_ALLOCS,
DEPOT_COUNTER_FREES,
DEPOT_COUNTER_INUSE,
DEPOT_COUNTER_FREELIST_SIZE,
DEPOT_COUNTER_COUNT,
};
static long counters[DEPOT_COUNTER_COUNT];
static const char *const counter_names[] = {
[DEPOT_COUNTER_ALLOCS] = "allocations",
[DEPOT_COUNTER_FREES] = "frees",
[DEPOT_COUNTER_INUSE] = "in_use",
[DEPOT_COUNTER_FREELIST_SIZE] = "freelist_size",
};
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 depot @pool, release all its entries to the freelist,
* and update the list of pools.
*/
static void depot_init_pool(void *pool)
{
int offset;
lockdep_assert_held(&pool_lock);
/* Initialize handles and link stack records into the freelist. */
for (offset = 0; offset <= DEPOT_POOL_SIZE - DEPOT_STACK_RECORD_SIZE;
offset += DEPOT_STACK_RECORD_SIZE) {
struct stack_record *stack = pool + offset;
stack->handle.pool_index = pools_num;
stack->handle.offset = offset >> DEPOT_STACK_ALIGN;
stack->handle.extra = 0;
/*
* Stack traces of size 0 are never saved, and we can simply use
* the size field as an indicator if this is a new unused stack
* record in the freelist.
*/
stack->size = 0;
INIT_LIST_HEAD(&stack->hash_list);
/*
* Add to the freelist front to prioritize never-used entries:
* required in case there are entries in the freelist, but their
* RCU cookie still belongs to the current RCU grace period
* (there can still be concurrent readers).
*/
list_add(&stack->free_list, &free_stacks);
counters[DEPOT_COUNTER_FREELIST_SIZE]++;
}
/* Save reference to the pool to be used by depot_fetch_stack(). */
stack_pools[pools_num] = pool;
/* Pairs with concurrent READ_ONCE() in depot_fetch_stack(). */
WRITE_ONCE(pools_num, pools_num + 1);
ASSERT_EXCLUSIVE_WRITER(pools_num);
}
/* 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_required)
return;
/*
* Use the preallocated memory for the new pool
* as long as we do not exceed the maximum number of pools.
*/
if (pools_num < DEPOT_MAX_POOLS) {
new_pool = *prealloc;
*prealloc = NULL;
}
/*
* At this point, either a new pool is kept or the maximum
* number of pools is reached. In either case, take note that
* keeping another pool is not required.
*/
WRITE_ONCE(new_pool_required, false);
}
/*
* Try to initialize a new stack depot pool from either a previous or the
* current pre-allocation, and release all its entries to the freelist.
*/
static bool depot_try_init_pool(void **prealloc)
{
lockdep_assert_held(&pool_lock);
/* Check if we have a new pool saved and use it. */
if (new_pool) {
depot_init_pool(new_pool);
new_pool = NULL;
/* Take note that we might need a new new_pool. */
if (pools_num < DEPOT_MAX_POOLS)
WRITE_ONCE(new_pool_required, true);
return true;
}
/* Bail out if we reached the pool limit. */
if (unlikely(pools_num >= DEPOT_MAX_POOLS)) {
WARN_ONCE(1, "Stack depot reached limit capacity");
return false;
}
/* Check if we have preallocated memory and use it. */
if (*prealloc) {
depot_init_pool(*prealloc);
*prealloc = NULL;
return true;
}
return false;
}
/* Try to find next free usable entry. */
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 (stack->size && !poll_state_synchronize_rcu(stack->rcu_state))
return NULL;
list_del(&stack->free_list);
counters[DEPOT_COUNTER_FREELIST_SIZE]--;
return stack;
}
/* 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;
lockdep_assert_held(&pool_lock);
/* This should already be checked by public API entry points. */
if (WARN_ON_ONCE(!size))
return NULL;
/* Check if we have a stack record to save the stack trace. */
stack = depot_pop_free();
if (!stack) {
/* No usable entries on the freelist - try to refill the freelist. */
if (!depot_try_init_pool(prealloc))
return NULL;
stack = depot_pop_free();
if (WARN_ON(!stack))
return NULL;
}
/* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */
if (size > CONFIG_STACKDEPOT_MAX_FRAMES)
size = CONFIG_STACKDEPOT_MAX_FRAMES;
/* Save the stack trace. */
stack->hash = hash;
stack->size = size;
/* stack->handle is already filled in by depot_init_pool(). */
refcount_set(&stack->count, 1);
memcpy(stack->entries, entries, flex_array_size(stack, entries, 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, DEPOT_STACK_RECORD_SIZE);
counters[DEPOT_COUNTER_ALLOCS]++;
counters[DEPOT_COUNTER_INUSE]++;
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;
size_t offset = parts.offset << DEPOT_STACK_ALIGN;
struct stack_record *stack;
lockdep_assert_not_held(&pool_lock);
if (parts.pool_index > pools_num_cached) {
WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
parts.pool_index, pools_num_cached, handle);
return NULL;
}
pool = stack_pools[parts.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_FREES]++;
counters[DEPOT_COUNTER_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_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);
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, &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);
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);