lib/stackdepot: various comments clean-ups
Clean up comments in include/linux/stackdepot.h and lib/stackdepot.c: 1. Rework the initialization comment in stackdepot.h. 2. Rework the header comment in stackdepot.c. 3. Various clean-ups for other comments. Also adjust whitespaces for find_stack and depot_alloc_stack call sites. No functional changes. Link: https://lkml.kernel.org/r/5836231b7954355e2311fc9b5870f697ea8e1f7d.1676063693.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Reviewed-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Andrey Konovalov
Andrew Morton
Родитель
beb3c23c69
Коммит
b232b9995a
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@ -1,11 +1,11 @@
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/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* A generic stack depot implementation
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* Stack depot - a stack trace storage that avoids duplication.
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*
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* Author: Alexander Potapenko <glider@google.com>
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* Copyright (C) 2016 Google, Inc.
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*
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* Based on code by Dmitry Chernenkov.
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* Based on the code by Dmitry Chernenkov.
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*/
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#ifndef _LINUX_STACKDEPOT_H
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@ -17,35 +17,37 @@ typedef u32 depot_stack_handle_t;
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/*
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* Number of bits in the handle that stack depot doesn't use. Users may store
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* information in them.
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* information in them via stack_depot_set/get_extra_bits.
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*/
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#define STACK_DEPOT_EXTRA_BITS 5
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/*
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* Every user of stack depot has to call stack_depot_init() during its own init
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* when it's decided that it will be calling stack_depot_save() later. This is
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* recommended for e.g. modules initialized later in the boot process, when
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* slab_is_available() is true.
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* Using stack depot requires its initialization, which can be done in 3 ways:
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*
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* The alternative is to select STACKDEPOT_ALWAYS_INIT to have stack depot
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* enabled as part of mm_init(), for subsystems where it's known at compile time
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* that stack depot will be used.
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* 1. Selecting CONFIG_STACKDEPOT_ALWAYS_INIT. This option is suitable in
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* scenarios where it's known at compile time that stack depot will be used.
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* Enabling this config makes the kernel initialize stack depot in mm_init().
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*
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* Another alternative is to call stack_depot_request_early_init(), when the
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* decision to use stack depot is taken e.g. when evaluating kernel boot
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* parameters, which precedes the enablement point in mm_init().
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* 2. Calling stack_depot_request_early_init() during early boot, before
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* stack_depot_early_init() in mm_init() completes. For example, this can
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* be done when evaluating kernel boot parameters.
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*
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* 3. Calling stack_depot_init(). Possible after boot is complete. This option
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* is recommended for modules initialized later in the boot process, after
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* mm_init() completes.
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*
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* stack_depot_init() and stack_depot_request_early_init() can be called
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* regardless of CONFIG_STACKDEPOT and are no-op when disabled. The actual
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* save/fetch/print functions should only be called from code that makes sure
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* CONFIG_STACKDEPOT is enabled.
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* regardless of whether CONFIG_STACKDEPOT is enabled and are no-op when this
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* config is disabled. The save/fetch/print stack depot functions can only be
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* called from the code that makes sure CONFIG_STACKDEPOT is enabled _and_
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* initializes stack depot via one of the ways listed above.
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*/
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#ifdef CONFIG_STACKDEPOT
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int stack_depot_init(void);
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void __init stack_depot_request_early_init(void);
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/* This is supposed to be called only from mm_init() */
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/* Must be only called from mm_init(). */
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int __init stack_depot_early_init(void);
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#else
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static inline int stack_depot_init(void) { return 0; }
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114
lib/stackdepot.c
114
lib/stackdepot.c
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@ -1,22 +1,26 @@
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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Generic stack depot for storing stack traces.
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* Stack depot - a stack trace storage that avoids duplication.
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*
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* Some debugging tools need to save stack traces of certain events which can
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* be later presented to the user. For example, KASAN needs to safe alloc and
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* free stacks for each object, but storing two stack traces per object
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* requires too much memory (e.g. SLUB_DEBUG needs 256 bytes per object for
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* that).
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* Stack depot is intended to be used by subsystems that need to store and
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* later retrieve many potentially duplicated stack traces without wasting
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* memory.
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*
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* Instead, stack depot maintains a hashtable of unique stacktraces. Since alloc
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* and free stacks repeat a lot, we save about 100x space.
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* Stacks are never removed from depot, so we store them contiguously one after
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* another in a contiguous memory allocation.
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* For example, KASAN needs to save allocation and free stack traces for each
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* object. Storing two stack traces per object requires a lot of memory (e.g.
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* SLUB_DEBUG needs 256 bytes per object for that). Since allocation and free
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* stack traces often repeat, using stack depot allows to save about 100x space.
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*
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* Internally, stack depot maintains a hash table of unique stacktraces. The
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* stack traces themselves are stored contiguously one after another in a set
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* of separate page allocations.
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*
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* Stack traces are never removed from stack depot.
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*
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* Author: Alexander Potapenko <glider@google.com>
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* Copyright (C) 2016 Google, Inc.
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*
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* Based on code by Dmitry Chernenkov.
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* Based on the code by Dmitry Chernenkov.
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*/
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#define pr_fmt(fmt) "stackdepot: " fmt
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@ -50,7 +54,7 @@
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(((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
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(1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)
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/* The compact structure to store the reference to stacks. */
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/* Compact structure that stores a reference to a stack. */
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union handle_parts {
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depot_stack_handle_t handle;
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struct {
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@ -63,10 +67,10 @@ union handle_parts {
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struct stack_record {
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struct stack_record *next; /* Link in the hash table */
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u32 hash; /* Hash in the hastable */
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u32 size; /* Number of frames in the stack */
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u32 hash; /* Hash in the hash table */
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u32 size; /* Number of stored frames */
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union handle_parts handle;
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unsigned long entries[]; /* Variable-sized array of entries. */
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unsigned long entries[]; /* Variable-sized array of frames */
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};
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static bool stack_depot_disabled;
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@ -317,7 +321,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
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return stack;
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}
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/* Calculate hash for a stack */
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/* Calculates the hash for a stack. */
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static inline u32 hash_stack(unsigned long *entries, unsigned int size)
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{
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return jhash2((u32 *)entries,
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@ -325,9 +329,9 @@ static inline u32 hash_stack(unsigned long *entries, unsigned int size)
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STACK_HASH_SEED);
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}
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/* Use our own, non-instrumented version of memcmp().
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*
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* We actually don't care about the order, just the equality.
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/*
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* Non-instrumented version of memcmp().
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* Does not check the lexicographical order, only the equality.
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*/
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static inline
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int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
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@ -340,7 +344,7 @@ int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
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return 0;
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}
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/* Find a stack that is equal to the one stored in entries in the hash */
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/* Finds a stack in a bucket of the hash table. */
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static inline struct stack_record *find_stack(struct stack_record *bucket,
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unsigned long *entries, int size,
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u32 hash)
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@ -357,27 +361,27 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
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}
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/**
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* __stack_depot_save - Save a stack trace from an array
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* __stack_depot_save - Save a stack trace to stack depot
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*
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* @entries: Pointer to storage array
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* @nr_entries: Size of the storage array
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* @alloc_flags: Allocation gfp flags
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* @entries: Pointer to the stack trace
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* @nr_entries: Number of frames in the stack
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* @alloc_flags: Allocation GFP flags
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* @can_alloc: Allocate stack pools (increased chance of failure if false)
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*
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* Saves a stack trace from @entries array of size @nr_entries. If @can_alloc is
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* %true, is allowed to replenish the stack pool in case no space is left
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* %true, stack depot can replenish the stack pools in case no space is left
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* (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids
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* any allocations and will fail if no space is left to store the stack trace.
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* any allocations and fails if no space is left to store the stack trace.
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*
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* If the stack trace in @entries is from an interrupt, only the portion up to
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* interrupt entry is saved.
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* If the provided stack trace comes from the interrupt context, only the part
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* up to the interrupt entry is saved.
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*
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* Context: Any context, but setting @can_alloc to %false is required if
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* alloc_pages() cannot be used from the current context. Currently
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* this is the case from contexts where neither %GFP_ATOMIC nor
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* this is the case for contexts where neither %GFP_ATOMIC nor
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* %GFP_NOWAIT can be used (NMI, raw_spin_lock).
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*
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* Return: The handle of the stack struct stored in depot, 0 on failure.
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* Return: Handle of the stack struct stored in depot, 0 on failure
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*/
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depot_stack_handle_t __stack_depot_save(unsigned long *entries,
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unsigned int nr_entries,
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@ -394,8 +398,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
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* If this stack trace is from an interrupt, including anything before
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* interrupt entry usually leads to unbounded stack depot growth.
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*
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* Because use of filter_irq_stacks() is a requirement to ensure
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* stackdepot can efficiently deduplicate interrupt stacks, always
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* Since use of filter_irq_stacks() is a requirement to ensure stack
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* depot can efficiently deduplicate interrupt stacks, always
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* filter_irq_stacks() to simplify all callers' use of stack depot.
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*/
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nr_entries = filter_irq_stacks(entries, nr_entries);
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@ -411,8 +415,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
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* The smp_load_acquire() here pairs with smp_store_release() to
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* |bucket| below.
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*/
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found = find_stack(smp_load_acquire(bucket), entries,
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nr_entries, hash);
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found = find_stack(smp_load_acquire(bucket), entries, nr_entries, hash);
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if (found)
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goto exit;
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@ -441,7 +444,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
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found = find_stack(*bucket, entries, nr_entries, hash);
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if (!found) {
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struct stack_record *new = depot_alloc_stack(entries, nr_entries, hash, &prealloc);
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struct stack_record *new =
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depot_alloc_stack(entries, nr_entries, hash, &prealloc);
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if (new) {
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new->next = *bucket;
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@ -454,8 +458,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
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}
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} else if (prealloc) {
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/*
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* We didn't need to store this stack trace, but let's keep
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* the preallocated memory for the future.
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* Stack depot already contains this stack trace, but let's
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* keep the preallocated memory for the future.
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*/
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depot_init_pool(&prealloc);
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}
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@ -463,7 +467,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
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raw_spin_unlock_irqrestore(&pool_lock, flags);
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exit:
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if (prealloc) {
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/* Nobody used this memory, ok to free it. */
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/* Stack depot didn't use this memory, free it. */
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free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
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}
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if (found)
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@ -474,16 +478,16 @@ fast_exit:
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EXPORT_SYMBOL_GPL(__stack_depot_save);
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/**
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* stack_depot_save - Save a stack trace from an array
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* stack_depot_save - Save a stack trace to stack depot
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*
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* @entries: Pointer to storage array
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* @nr_entries: Size of the storage array
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* @alloc_flags: Allocation gfp flags
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* @entries: Pointer to the stack trace
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* @nr_entries: Number of frames in the stack
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* @alloc_flags: Allocation GFP flags
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*
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* Context: Contexts where allocations via alloc_pages() are allowed.
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* See __stack_depot_save() for more details.
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*
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* Return: The handle of the stack struct stored in depot, 0 on failure.
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* Return: Handle of the stack trace stored in depot, 0 on failure
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*/
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depot_stack_handle_t stack_depot_save(unsigned long *entries,
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unsigned int nr_entries,
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@ -494,13 +498,12 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
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EXPORT_SYMBOL_GPL(stack_depot_save);
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/**
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* stack_depot_fetch - Fetch stack entries from a depot
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* stack_depot_fetch - Fetch a stack trace from stack depot
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*
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* @handle: Stack depot handle which was returned from
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* stack_depot_save().
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* @entries: Pointer to store the entries address
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* @handle: Stack depot handle returned from stack_depot_save()
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* @entries: Pointer to store the address of the stack trace
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*
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* Return: The number of trace entries for this depot.
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* Return: Number of frames for the fetched stack
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*/
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unsigned int stack_depot_fetch(depot_stack_handle_t handle,
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unsigned long **entries)
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@ -535,11 +538,9 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
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EXPORT_SYMBOL_GPL(stack_depot_fetch);
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/**
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* stack_depot_print - print stack entries from a depot
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*
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* @stack: Stack depot handle which was returned from
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* stack_depot_save().
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* stack_depot_print - Print a stack trace from stack depot
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*
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* @stack: Stack depot handle returned from stack_depot_save()
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*/
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void stack_depot_print(depot_stack_handle_t stack)
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{
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@ -553,17 +554,14 @@ void stack_depot_print(depot_stack_handle_t stack)
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EXPORT_SYMBOL_GPL(stack_depot_print);
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/**
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* stack_depot_snprint - print stack entries from a depot into a buffer
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* stack_depot_snprint - Print a stack trace from stack depot into a buffer
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*
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* @handle: Stack depot handle which was returned from
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* stack_depot_save().
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* @handle: Stack depot handle returned from stack_depot_save()
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* @buf: Pointer to the print buffer
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*
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* @size: Size of the print buffer
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*
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* @spaces: Number of leading spaces to print
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*
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* Return: Number of bytes printed.
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* Return: Number of bytes printed
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*/
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int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
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int spaces)
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