/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
- * A generic stack depot implementation
+ * 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.
+ *
+ * Stack traces are never removed from the stack depot.
*
* Author: Alexander Potapenko <glider@google.com>
* Copyright (C) 2016 Google, Inc.
*
- * Based on code by Dmitry Chernenkov.
+ * Based on the code by Dmitry Chernenkov.
*/
#ifndef _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.
+ * information in them via stack_depot_set/get_extra_bits.
*/
#define STACK_DEPOT_EXTRA_BITS 5
-depot_stack_handle_t __stack_depot_save(unsigned long *entries,
- unsigned int nr_entries,
- unsigned int extra_bits,
- gfp_t gfp_flags, bool can_alloc);
-
/*
- * Every user of stack depot has to call stack_depot_init() during its own init
- * when it's decided that it will be calling stack_depot_save() later. This is
- * recommended for e.g. modules initialized later in the boot process, when
- * slab_is_available() is true.
- *
- * The alternative is to select STACKDEPOT_ALWAYS_INIT to have stack depot
- * enabled as part of mm_init(), for subsystems where it's known at compile time
- * that stack depot will be used.
- *
- * Another alternative is to call stack_depot_want_early_init(), when the
- * decision to use stack depot is taken e.g. when evaluating kernel boot
- * parameters, which precedes the enablement point in mm_init().
- *
- * stack_depot_init() and stack_depot_want_early_init() can be called regardless
- * of CONFIG_STACKDEPOT and are no-op when disabled. The actual save/fetch/print
- * functions should only be called from code that makes sure CONFIG_STACKDEPOT
- * is enabled.
+ * 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_want_early_init(void);
+void __init stack_depot_request_early_init(void);
-/* This is supposed to be called only from mm_init() */
+/* 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_want_early_init(void) { }
+static inline void stack_depot_request_early_init(void) { }
static inline int stack_depot_early_init(void) { return 0; }
#endif
+/**
+ * __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
+ * @can_alloc: Allocate stack pools (increased chance of failure if false)
+ *
+ * Saves a stack trace from @entries array of size @nr_entries. If @can_alloc is
+ * %true, stack depot can replenish the stack pools in case no space is left
+ * (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids
+ * any allocations and fails if no space is left to store the stack trace.
+ *
+ * If the provided stack trace comes from the interrupt context, only the part
+ * up to the interrupt entry is saved.
+ *
+ * Context: Any context, but setting @can_alloc to %false 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(unsigned long *entries,
+ unsigned int nr_entries,
+ gfp_t gfp_flags, bool can_alloc);
+
+/**
+ * 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
+ *
+ * Context: Contexts where allocations via alloc_pages() are allowed.
+ * See __stack_depot_save() 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 gfp_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);
-unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle);
+/**
+ * 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);
-void stack_depot_print(depot_stack_handle_t stack);
+/**
+ * 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