1 /* SPDX-License-Identifier: GPL-2.0-or-later */ 2 /* 3 * Stack depot - a stack trace storage that avoids duplication. 4 * 5 * Stack depot is intended to be used by subsystems that need to store and 6 * later retrieve many potentially duplicated stack traces without wasting 7 * memory. 8 * 9 * For example, KASAN needs to save allocation and free stack traces for each 10 * object. Storing two stack traces per object requires a lot of memory (e.g. 11 * SLUB_DEBUG needs 256 bytes per object for that). Since allocation and free 12 * stack traces often repeat, using stack depot allows to save about 100x space. 13 * 14 * Stack traces are never removed from the stack depot. 15 * 16 * Author: Alexander Potapenko <[email protected]> 17 * Copyright (C) 2016 Google, Inc. 18 * 19 * Based on the code by Dmitry Chernenkov. 20 */ 21 22 #ifndef _LINUX_STACKDEPOT_H 23 #define _LINUX_STACKDEPOT_H 24 25 #include <linux/gfp.h> 26 27 typedef u32 depot_stack_handle_t; 28 29 /* 30 * Number of bits in the handle that stack depot doesn't use. Users may store 31 * information in them via stack_depot_set/get_extra_bits. 32 */ 33 #define STACK_DEPOT_EXTRA_BITS 5 34 35 typedef u32 depot_flags_t; 36 37 /* 38 * Flags that can be passed to stack_depot_save_flags(); see the comment next 39 * to its declaration for more details. 40 */ 41 #define STACK_DEPOT_FLAG_CAN_ALLOC ((depot_flags_t)0x0001) 42 43 #define STACK_DEPOT_FLAGS_NUM 1 44 #define STACK_DEPOT_FLAGS_MASK ((depot_flags_t)((1 << STACK_DEPOT_FLAGS_NUM) - 1)) 45 46 /* 47 * Using stack depot requires its initialization, which can be done in 3 ways: 48 * 49 * 1. Selecting CONFIG_STACKDEPOT_ALWAYS_INIT. This option is suitable in 50 * scenarios where it's known at compile time that stack depot will be used. 51 * Enabling this config makes the kernel initialize stack depot in mm_init(). 52 * 53 * 2. Calling stack_depot_request_early_init() during early boot, before 54 * stack_depot_early_init() in mm_init() completes. For example, this can 55 * be done when evaluating kernel boot parameters. 56 * 57 * 3. Calling stack_depot_init(). Possible after boot is complete. This option 58 * is recommended for modules initialized later in the boot process, after 59 * mm_init() completes. 60 * 61 * stack_depot_init() and stack_depot_request_early_init() can be called 62 * regardless of whether CONFIG_STACKDEPOT is enabled and are no-op when this 63 * config is disabled. The save/fetch/print stack depot functions can only be 64 * called from the code that makes sure CONFIG_STACKDEPOT is enabled _and_ 65 * initializes stack depot via one of the ways listed above. 66 */ 67 #ifdef CONFIG_STACKDEPOT 68 int stack_depot_init(void); 69 70 void __init stack_depot_request_early_init(void); 71 72 /* Must be only called from mm_init(). */ 73 int __init stack_depot_early_init(void); 74 #else 75 static inline int stack_depot_init(void) { return 0; } 76 77 static inline void stack_depot_request_early_init(void) { } 78 79 static inline int stack_depot_early_init(void) { return 0; } 80 #endif 81 82 /** 83 * stack_depot_save_flags - Save a stack trace to stack depot 84 * 85 * @entries: Pointer to the stack trace 86 * @nr_entries: Number of frames in the stack 87 * @alloc_flags: Allocation GFP flags 88 * @depot_flags: Stack depot flags 89 * 90 * Saves a stack trace from @entries array of size @nr_entries. 91 * 92 * If STACK_DEPOT_FLAG_CAN_ALLOC is set in @depot_flags, stack depot can 93 * replenish the stack pools in case no space is left (allocates using GFP 94 * flags of @alloc_flags). Otherwise, stack depot avoids any allocations and 95 * fails if no space is left to store the stack trace. 96 * 97 * If the provided stack trace comes from the interrupt context, only the part 98 * up to the interrupt entry is saved. 99 * 100 * Context: Any context, but setting STACK_DEPOT_FLAG_CAN_ALLOC is required if 101 * alloc_pages() cannot be used from the current context. Currently 102 * this is the case for contexts where neither %GFP_ATOMIC nor 103 * %GFP_NOWAIT can be used (NMI, raw_spin_lock). 104 * 105 * Return: Handle of the stack struct stored in depot, 0 on failure 106 */ 107 depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, 108 unsigned int nr_entries, 109 gfp_t gfp_flags, 110 depot_flags_t depot_flags); 111 112 /** 113 * stack_depot_save - Save a stack trace to stack depot 114 * 115 * @entries: Pointer to the stack trace 116 * @nr_entries: Number of frames in the stack 117 * @alloc_flags: Allocation GFP flags 118 * 119 * Context: Contexts where allocations via alloc_pages() are allowed. 120 * See stack_depot_save_flags() for more details. 121 * 122 * Return: Handle of the stack trace stored in depot, 0 on failure 123 */ 124 depot_stack_handle_t stack_depot_save(unsigned long *entries, 125 unsigned int nr_entries, gfp_t gfp_flags); 126 127 /** 128 * stack_depot_fetch - Fetch a stack trace from stack depot 129 * 130 * @handle: Stack depot handle returned from stack_depot_save() 131 * @entries: Pointer to store the address of the stack trace 132 * 133 * Return: Number of frames for the fetched stack 134 */ 135 unsigned int stack_depot_fetch(depot_stack_handle_t handle, 136 unsigned long **entries); 137 138 /** 139 * stack_depot_print - Print a stack trace from stack depot 140 * 141 * @stack: Stack depot handle returned from stack_depot_save() 142 */ 143 void stack_depot_print(depot_stack_handle_t stack); 144 145 /** 146 * stack_depot_snprint - Print a stack trace from stack depot into a buffer 147 * 148 * @handle: Stack depot handle returned from stack_depot_save() 149 * @buf: Pointer to the print buffer 150 * @size: Size of the print buffer 151 * @spaces: Number of leading spaces to print 152 * 153 * Return: Number of bytes printed 154 */ 155 int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size, 156 int spaces); 157 158 /** 159 * stack_depot_set_extra_bits - Set extra bits in a stack depot handle 160 * 161 * @handle: Stack depot handle returned from stack_depot_save() 162 * @extra_bits: Value to set the extra bits 163 * 164 * Return: Stack depot handle with extra bits set 165 * 166 * Stack depot handles have a few unused bits, which can be used for storing 167 * user-specific information. These bits are transparent to the stack depot. 168 */ 169 depot_stack_handle_t __must_check stack_depot_set_extra_bits( 170 depot_stack_handle_t handle, unsigned int extra_bits); 171 172 /** 173 * stack_depot_get_extra_bits - Retrieve extra bits from a stack depot handle 174 * 175 * @handle: Stack depot handle with extra bits saved 176 * 177 * Return: Extra bits retrieved from the stack depot handle 178 */ 179 unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle); 180 181 #endif 182