include/linux/stackdepot.h

   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  * Author: Alexander Potapenko <glider@google.com>
  15  * Copyright (C) 2016 Google, Inc.
  16  *
  17  * Based on the code by Dmitry Chernenkov.
  18  */
  19
  20 #ifndef _LINUX_STACKDEPOT_H
  21 #define _LINUX_STACKDEPOT_H
  22
  23 #include <linux/gfp.h>
  24
  25 typedef u32 depot_stack_handle_t;
  26
  27 /*
  28  * Number of bits in the handle that stack depot doesn't use. Users may store
  29  * information in them via stack_depot_set/get_extra_bits.
  30  */
  31 #define STACK_DEPOT_EXTRA_BITS 5
  32
  33 #define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
  34
  35 #define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
  36 #define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
  37 #define DEPOT_STACK_ALIGN 4
  38 #define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
  39 #define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
  40                                STACK_DEPOT_EXTRA_BITS)
  41
  42 #ifdef CONFIG_STACKDEPOT
  43 /* Compact structure that stores a reference to a stack. */
  44 union handle_parts {
  45         depot_stack_handle_t handle;
  46         struct {
  47                 u32 pool_index_plus_1   : DEPOT_POOL_INDEX_BITS;
  48                 u32 offset              : DEPOT_OFFSET_BITS;
  49                 u32 extra               : STACK_DEPOT_EXTRA_BITS;
  50         };
  51 };
  52
  53 struct stack_record {
  54         struct list_head hash_list;     /* Links in the hash table */
  55         u32 hash;                       /* Hash in hash table */
  56         u32 size;                       /* Number of stored frames */
  57         union handle_parts handle;      /* Constant after initialization */
  58         refcount_t count;
  59         union {
  60                 unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES];    /* Frames */
  61                 struct {
  62                         /*
  63                          * An important invariant of the implementation is to
  64                          * only place a stack record onto the freelist iff its
  65                          * refcount is zero. Because stack records with a zero
  66                          * refcount are never considered as valid, it is safe to
  67                          * union @entries and freelist management state below.
  68                          * Conversely, as soon as an entry is off the freelist
  69                          * and its refcount becomes non-zero, the below must not
  70                          * be accessed until being placed back on the freelist.
  71                          */
  72                         struct list_head free_list;     /* Links in the freelist */
  73                         unsigned long rcu_state;        /* RCU cookie */
  74                 };
  75         };
  76 };
  77 #endif
  78
  79 typedef u32 depot_flags_t;
  80
  81 /*
  82  * Flags that can be passed to stack_depot_save_flags(); see the comment next
  83  * to its declaration for more details.
  84  */
  85 #define STACK_DEPOT_FLAG_CAN_ALLOC      ((depot_flags_t)0x0001)
  86 #define STACK_DEPOT_FLAG_GET            ((depot_flags_t)0x0002)
  87
  88 #define STACK_DEPOT_FLAGS_NUM   2
  89 #define STACK_DEPOT_FLAGS_MASK  ((depot_flags_t)((1 << STACK_DEPOT_FLAGS_NUM) - 1))
  90
  91 /*
  92  * Using stack depot requires its initialization, which can be done in 3 ways:
  93  *
  94  * 1. Selecting CONFIG_STACKDEPOT_ALWAYS_INIT. This option is suitable in
  95  *    scenarios where it's known at compile time that stack depot will be used.
  96  *    Enabling this config makes the kernel initialize stack depot in mm_init().
  97  *
  98  * 2. Calling stack_depot_request_early_init() during early boot, before
  99  *    stack_depot_early_init() in mm_init() completes. For example, this can
 100  *    be done when evaluating kernel boot parameters.
 101  *
 102  * 3. Calling stack_depot_init(). Possible after boot is complete. This option
 103  *    is recommended for modules initialized later in the boot process, after
 104  *    mm_init() completes.
 105  *
 106  * stack_depot_init() and stack_depot_request_early_init() can be called
 107  * regardless of whether CONFIG_STACKDEPOT is enabled and are no-op when this
 108  * config is disabled. The save/fetch/print stack depot functions can only be
 109  * called from the code that makes sure CONFIG_STACKDEPOT is enabled _and_
 110  * initializes stack depot via one of the ways listed above.
 111  */
 112 #ifdef CONFIG_STACKDEPOT
 113 int stack_depot_init(void);
 114
 115 void __init stack_depot_request_early_init(void);
 116
 117 /* Must be only called from mm_init(). */
 118 int __init stack_depot_early_init(void);
 119 #else
 120 static inline int stack_depot_init(void) { return 0; }
 121
 122 static inline void stack_depot_request_early_init(void) { }
 123
 124 static inline int stack_depot_early_init(void)  { return 0; }
 125 #endif
 126
 127 /**
 128  * stack_depot_save_flags - Save a stack trace to stack depot
 129  *
 130  * @entries:            Pointer to the stack trace
 131  * @nr_entries:         Number of frames in the stack
 132  * @alloc_flags:        Allocation GFP flags
 133  * @depot_flags:        Stack depot flags
 134  *
 135  * Saves a stack trace from @entries array of size @nr_entries.
 136  *
 137  * If STACK_DEPOT_FLAG_CAN_ALLOC is set in @depot_flags, stack depot can
 138  * replenish the stack pools in case no space is left (allocates using GFP
 139  * flags of @alloc_flags). Otherwise, stack depot avoids any allocations and
 140  * fails if no space is left to store the stack trace.
 141  *
 142  * If STACK_DEPOT_FLAG_GET is set in @depot_flags, stack depot will increment
 143  * the refcount on the saved stack trace if it already exists in stack depot.
 144  * Users of this flag must also call stack_depot_put() when keeping the stack
 145  * trace is no longer required to avoid overflowing the refcount.
 146  *
 147  * If the provided stack trace comes from the interrupt context, only the part
 148  * up to the interrupt entry is saved.
 149  *
 150  * Context: Any context, but setting STACK_DEPOT_FLAG_CAN_ALLOC is required if
 151  *          alloc_pages() cannot be used from the current context. Currently
 152  *          this is the case for contexts where neither %GFP_ATOMIC nor
 153  *          %GFP_NOWAIT can be used (NMI, raw_spin_lock).
 154  *
 155  * Return: Handle of the stack struct stored in depot, 0 on failure
 156  */
 157 depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
 158                                             unsigned int nr_entries,
 159                                             gfp_t gfp_flags,
 160                                             depot_flags_t depot_flags);
 161
 162 /**
 163  * stack_depot_save - Save a stack trace to stack depot
 164  *
 165  * @entries:            Pointer to the stack trace
 166  * @nr_entries:         Number of frames in the stack
 167  * @alloc_flags:        Allocation GFP flags
 168  *
 169  * Does not increment the refcount on the saved stack trace; see
 170  * stack_depot_save_flags() for more details.
 171  *
 172  * Context: Contexts where allocations via alloc_pages() are allowed;
 173  *          see stack_depot_save_flags() for more details.
 174  *
 175  * Return: Handle of the stack trace stored in depot, 0 on failure
 176  */
 177 depot_stack_handle_t stack_depot_save(unsigned long *entries,
 178                                       unsigned int nr_entries, gfp_t gfp_flags);
 179
 180 /**
 181  * __stack_depot_get_stack_record - Get a pointer to a stack_record struct
 182  *
 183  * @handle: Stack depot handle
 184  *
 185  * This function is only for internal purposes.
 186  *
 187  * Return: Returns a pointer to a stack_record struct
 188  */
 189 struct stack_record *__stack_depot_get_stack_record(depot_stack_handle_t handle);
 190
 191 /**
 192  * stack_depot_fetch - Fetch a stack trace from stack depot
 193  *
 194  * @handle:     Stack depot handle returned from stack_depot_save()
 195  * @entries:    Pointer to store the address of the stack trace
 196  *
 197  * Return: Number of frames for the fetched stack
 198  */
 199 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 200                                unsigned long **entries);
 201
 202 /**
 203  * stack_depot_print - Print a stack trace from stack depot
 204  *
 205  * @stack:      Stack depot handle returned from stack_depot_save()
 206  */
 207 void stack_depot_print(depot_stack_handle_t stack);
 208
 209 /**
 210  * stack_depot_snprint - Print a stack trace from stack depot into a buffer
 211  *
 212  * @handle:     Stack depot handle returned from stack_depot_save()
 213  * @buf:        Pointer to the print buffer
 214  * @size:       Size of the print buffer
 215  * @spaces:     Number of leading spaces to print
 216  *
 217  * Return:      Number of bytes printed
 218  */
 219 int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
 220                        int spaces);
 221
 222 /**
 223  * stack_depot_put - Drop a reference to a stack trace from stack depot
 224  *
 225  * @handle:     Stack depot handle returned from stack_depot_save()
 226  *
 227  * The stack trace is evicted from stack depot once all references to it have
 228  * been dropped (once the number of stack_depot_evict() calls matches the
 229  * number of stack_depot_save_flags() calls with STACK_DEPOT_FLAG_GET set for
 230  * this stack trace).
 231  */
 232 void stack_depot_put(depot_stack_handle_t handle);
 233
 234 /**
 235  * stack_depot_set_extra_bits - Set extra bits in a stack depot handle
 236  *
 237  * @handle:     Stack depot handle returned from stack_depot_save()
 238  * @extra_bits: Value to set the extra bits
 239  *
 240  * Return: Stack depot handle with extra bits set
 241  *
 242  * Stack depot handles have a few unused bits, which can be used for storing
 243  * user-specific information. These bits are transparent to the stack depot.
 244  */
 245 depot_stack_handle_t __must_check stack_depot_set_extra_bits(
 246                         depot_stack_handle_t handle, unsigned int extra_bits);
 247
 248 /**
 249  * stack_depot_get_extra_bits - Retrieve extra bits from a stack depot handle
 250  *
 251  * @handle:     Stack depot handle with extra bits saved
 252  *
 253  * Return: Extra bits retrieved from the stack depot handle
 254  */
 255 unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle);
 256
 257 #endif