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/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Stack depot - a stack trace storage that avoids duplication.
*
* Stack depot is intended to be used by subsystems that need to store and
* later retrieve many potentially duplicated stack traces without wasting
* memory.
*
* For example, KASAN needs to save allocation and free stack traces for each
* object. Storing two stack traces per object requires a lot of memory (e.g.
* SLUB_DEBUG needs 256 bytes per object for that). Since allocation and free
* stack traces often repeat, using stack depot allows to save about 100x space.
*
* Author: Alexander Potapenko <glider@google.com>
* Copyright (C) 2016 Google, Inc.
*
* Based on the code by Dmitry Chernenkov.
*/
#ifndef _LINUX_STACKDEPOT_H
#define _LINUX_STACKDEPOT_H
#include <linux/gfp.h>
typedef u32 depot_stack_handle_t;
/*
* Number of bits in the handle that stack depot doesn't use. Users may store
* information in them via stack_depot_set/get_extra_bits.
*/
#define STACK_DEPOT_EXTRA_BITS 5
#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)
#ifdef CONFIG_STACKDEPOT
/* Compact structure that stores a reference to a stack. */
union handle_parts {
depot_stack_handle_t handle;
struct {
u32 pool_index_plus_1 : 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 */
};
};
};
#endif
typedef u32 depot_flags_t;
/*
* Flags that can be passed to stack_depot_save_flags(); see the comment next
* to its declaration for more details.
*/
#define STACK_DEPOT_FLAG_CAN_ALLOC ((depot_flags_t)0x0001)
#define STACK_DEPOT_FLAG_GET ((depot_flags_t)0x0002)
#define STACK_DEPOT_FLAGS_NUM 2
#define STACK_DEPOT_FLAGS_MASK ((depot_flags_t)((1 << STACK_DEPOT_FLAGS_NUM) - 1))
/*
* Using stack depot requires its initialization, which can be done in 3 ways:
*
* 1. Selecting CONFIG_STACKDEPOT_ALWAYS_INIT. This option is suitable in
* scenarios where it's known at compile time that stack depot will be used.
* Enabling this config makes the kernel initialize stack depot in mm_init().
*
* 2. Calling stack_depot_request_early_init() during early boot, before
* stack_depot_early_init() in mm_init() completes. For example, this can
* be done when evaluating kernel boot parameters.
*
* 3. Calling stack_depot_init(). Possible after boot is complete. This option
* is recommended for modules initialized later in the boot process, after
* mm_init() completes.
*
* stack_depot_init() and stack_depot_request_early_init() can be called
* regardless of whether CONFIG_STACKDEPOT is enabled and are no-op when this
* config is disabled. The save/fetch/print stack depot functions can only be
* called from the code that makes sure CONFIG_STACKDEPOT is enabled _and_
* initializes stack depot via one of the ways listed above.
*/
#ifdef CONFIG_STACKDEPOT
int stack_depot_init(void);
void __init stack_depot_request_early_init(void);
/* Must be only called from mm_init(). */
int __init stack_depot_early_init(void);
#else
static inline int stack_depot_init(void) { return 0; }
static inline void stack_depot_request_early_init(void) { }
static inline int stack_depot_early_init(void) { return 0; }
#endif
/**
* stack_depot_save_flags - Save a stack trace to stack depot
*
* @entries: Pointer to the stack trace
* @nr_entries: Number of frames in the stack
* @alloc_flags: Allocation GFP flags
* @depot_flags: Stack depot flags
*
* Saves a stack trace from @entries array of size @nr_entries.
*
* If STACK_DEPOT_FLAG_CAN_ALLOC is set in @depot_flags, stack depot can
* replenish the stack pools in case no space is left (allocates using GFP
* flags of @alloc_flags). Otherwise, stack depot avoids any allocations and
* fails if no space is left to store the stack trace.
*
* If STACK_DEPOT_FLAG_GET is set in @depot_flags, stack depot will increment
* the refcount on the saved stack trace if it already exists in stack depot.
* Users of this flag must also call stack_depot_put() when keeping the stack
* trace is no longer required to avoid overflowing the refcount.
*
* If the provided stack trace comes from the interrupt context, only the part
* up to the interrupt entry is saved.
*
* Context: Any context, but unsetting STACK_DEPOT_FLAG_CAN_ALLOC is required if
* alloc_pages() cannot be used from the current context. Currently
* this is the case for contexts where neither %GFP_ATOMIC nor
* %GFP_NOWAIT can be used (NMI, raw_spin_lock).
*
* Return: Handle of the stack struct stored in depot, 0 on failure
*/
depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
unsigned int nr_entries,
gfp_t alloc_flags,
depot_flags_t depot_flags);
/**
* stack_depot_save - Save a stack trace to stack depot
*
* @entries: Pointer to the stack trace
* @nr_entries: Number of frames in the stack
* @alloc_flags: Allocation GFP flags
*
* Does not increment the refcount on the saved stack trace; see
* stack_depot_save_flags() for more details.
*
* Context: Contexts where allocations via alloc_pages() are allowed;
* see stack_depot_save_flags() for more details.
*
* Return: Handle of the stack trace stored in depot, 0 on failure
*/
depot_stack_handle_t stack_depot_save(unsigned long *entries,
unsigned int nr_entries, gfp_t alloc_flags);
/**
* stack_depot_fetch - Fetch a stack trace from stack depot
*
* @handle: Stack depot handle returned from stack_depot_save()
* @entries: Pointer to store the address of the stack trace
*
* Return: Number of frames for the fetched stack
*/
unsigned int stack_depot_fetch(depot_stack_handle_t handle,
unsigned long **entries);
/**
* stack_depot_print - Print a stack trace from stack depot
*
* @stack: Stack depot handle returned from stack_depot_save()
*/
void stack_depot_print(depot_stack_handle_t stack);
/**
* stack_depot_snprint - Print a stack trace from stack depot into a buffer
*
* @handle: Stack depot handle returned from stack_depot_save()
* @buf: Pointer to the print buffer
* @size: Size of the print buffer
* @spaces: Number of leading spaces to print
*
* Return: Number of bytes printed
*/
int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
int spaces);
/**
* stack_depot_put - Drop a reference to a stack trace from stack depot
*
* @handle: Stack depot handle returned from stack_depot_save()
*
* The stack trace is evicted from stack depot once all references to it have
* been dropped (once the number of stack_depot_evict() calls matches the
* number of stack_depot_save_flags() calls with STACK_DEPOT_FLAG_GET set for
* this stack trace).
*/
void stack_depot_put(depot_stack_handle_t handle);
/**
* stack_depot_set_extra_bits - Set extra bits in a stack depot handle
*
* @handle: Stack depot handle returned from stack_depot_save()
* @extra_bits: Value to set the extra bits
*
* Return: Stack depot handle with extra bits set
*
* Stack depot handles have a few unused bits, which can be used for storing
* user-specific information. These bits are transparent to the stack depot.
*/
depot_stack_handle_t __must_check stack_depot_set_extra_bits(
depot_stack_handle_t handle, unsigned int extra_bits);
/**
* stack_depot_get_extra_bits - Retrieve extra bits from a stack depot handle
*
* @handle: Stack depot handle with extra bits saved
*
* Return: Extra bits retrieved from the stack depot handle
*/
unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle);
#endif