https://github.com/torvalds/linux
Tip revision: f1fcbaa18b28dec10281551dfe6ed3a3ed80e3d6 authored by Linus Torvalds on 14 May 2023, 19:51:40 UTC
Linux 6.4-rc2
Linux 6.4-rc2
Tip revision: f1fcbaa
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/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);