From b232b9995a6dbaafe19d07d81acc039bc84bd569 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Fri, 10 Feb 2023 22:16:05 +0100 Subject: [PATCH] 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 Reviewed-by: Alexander Potapenko Signed-off-by: Andrew Morton --- include/linux/stackdepot.h | 36 +++++------ lib/stackdepot.c | 120 ++++++++++++++++++------------------- 2 files changed, 78 insertions(+), 78 deletions(-) diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h index 267f4b2634ee..afdf8ee7b597 100644 --- a/include/linux/stackdepot.h +++ b/include/linux/stackdepot.h @@ -1,11 +1,11 @@ /* SPDX-License-Identifier: GPL-2.0-or-later */ /* - * A generic stack depot implementation + * Stack depot - a stack trace storage that avoids duplication. * * Author: Alexander Potapenko * Copyright (C) 2016 Google, Inc. * - * Based on code by Dmitry Chernenkov. + * Based on the code by Dmitry Chernenkov. */ #ifndef _LINUX_STACKDEPOT_H @@ -17,35 +17,37 @@ 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 /* - * 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. + * Using stack depot requires its initialization, which can be done in 3 ways: * - * 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. + * 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(). * - * Another alternative is to call stack_depot_request_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(). + * 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 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. + * 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); -/* 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; } diff --git a/lib/stackdepot.c b/lib/stackdepot.c index b625090890e1..aaa5d2f1abc2 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -1,22 +1,26 @@ // SPDX-License-Identifier: GPL-2.0-only /* - * Generic stack depot for storing stack traces. + * Stack depot - a stack trace storage that avoids duplication. * - * Some debugging tools need to save stack traces of certain events which can - * be later presented to the user. For example, KASAN needs to safe alloc and - * free stacks for each object, but storing two stack traces per object - * requires too much memory (e.g. SLUB_DEBUG needs 256 bytes per object for - * that). + * Stack depot is intended to be used by subsystems that need to store and + * later retrieve many potentially duplicated stack traces without wasting + * memory. * - * Instead, stack depot maintains a hashtable of unique stacktraces. Since alloc - * and free stacks repeat a lot, we save about 100x space. - * Stacks are never removed from depot, so we store them contiguously one after - * another in a contiguous memory allocation. + * 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. + * + * Internally, stack depot maintains a hash table of unique stacktraces. The + * stack traces themselves are stored contiguously one after another in a set + * of separate page allocations. + * + * Stack traces are never removed from stack depot. * * Author: Alexander Potapenko * Copyright (C) 2016 Google, Inc. * - * Based on code by Dmitry Chernenkov. + * Based on the code by Dmitry Chernenkov. */ #define pr_fmt(fmt) "stackdepot: " fmt @@ -50,7 +54,7 @@ (((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \ (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP) -/* The compact structure to store the reference to stacks. */ +/* Compact structure that stores a reference to a stack. */ union handle_parts { depot_stack_handle_t handle; struct { @@ -62,11 +66,11 @@ union handle_parts { }; struct stack_record { - struct stack_record *next; /* Link in the hashtable */ - u32 hash; /* Hash in the hastable */ - u32 size; /* Number of frames in the stack */ + struct stack_record *next; /* Link in the hash table */ + u32 hash; /* Hash in the hash table */ + u32 size; /* Number of stored frames */ union handle_parts handle; - unsigned long entries[]; /* Variable-sized array of entries. */ + unsigned long entries[]; /* Variable-sized array of frames */ }; static bool stack_depot_disabled; @@ -317,7 +321,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc) return stack; } -/* Calculate hash for a stack */ +/* Calculates the hash for a stack. */ static inline u32 hash_stack(unsigned long *entries, unsigned int size) { return jhash2((u32 *)entries, @@ -325,9 +329,9 @@ static inline u32 hash_stack(unsigned long *entries, unsigned int size) STACK_HASH_SEED); } -/* Use our own, non-instrumented version of memcmp(). - * - * We actually don't care about the order, just the equality. +/* + * Non-instrumented version of memcmp(). + * Does not check the lexicographical order, only the equality. */ static inline int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, @@ -340,7 +344,7 @@ int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, return 0; } -/* Find a stack that is equal to the one stored in entries in the hash */ +/* Finds a stack in a bucket of the hash table. */ static inline struct stack_record *find_stack(struct stack_record *bucket, unsigned long *entries, int size, u32 hash) @@ -357,27 +361,27 @@ static inline struct stack_record *find_stack(struct stack_record *bucket, } /** - * __stack_depot_save - Save a stack trace from an array + * __stack_depot_save - Save a stack trace to stack depot * - * @entries: Pointer to storage array - * @nr_entries: Size of the storage array - * @alloc_flags: Allocation gfp flags + * @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, is allowed to replenish the stack pool in case no space is left + * %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 will fail if no space is left to store the stack trace. + * any allocations and fails if no space is left to store the stack trace. * - * If the stack trace in @entries is from an interrupt, only the portion up to - * interrupt entry is saved. + * 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 from contexts where neither %GFP_ATOMIC nor + * this is the case for contexts where neither %GFP_ATOMIC nor * %GFP_NOWAIT can be used (NMI, raw_spin_lock). * - * Return: The handle of the stack struct stored in depot, 0 on failure. + * 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, @@ -392,11 +396,11 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, /* * If this stack trace is from an interrupt, including anything before - * interrupt entry usually leads to unbounded stackdepot growth. + * interrupt entry usually leads to unbounded stack depot growth. * - * Because use of filter_irq_stacks() is a requirement to ensure - * stackdepot can efficiently deduplicate interrupt stacks, always - * filter_irq_stacks() to simplify all callers' use of stackdepot. + * Since use of filter_irq_stacks() is a requirement to ensure stack + * depot can efficiently deduplicate interrupt stacks, always + * filter_irq_stacks() to simplify all callers' use of stack depot. */ nr_entries = filter_irq_stacks(entries, nr_entries); @@ -411,8 +415,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, * The smp_load_acquire() here pairs with smp_store_release() to * |bucket| below. */ - found = find_stack(smp_load_acquire(bucket), entries, - nr_entries, hash); + found = find_stack(smp_load_acquire(bucket), entries, nr_entries, hash); if (found) goto exit; @@ -441,7 +444,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, found = find_stack(*bucket, entries, nr_entries, hash); if (!found) { - struct stack_record *new = depot_alloc_stack(entries, nr_entries, hash, &prealloc); + struct stack_record *new = + depot_alloc_stack(entries, nr_entries, hash, &prealloc); if (new) { new->next = *bucket; @@ -454,8 +458,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, } } else if (prealloc) { /* - * We didn't need to store this stack trace, but let's keep - * the preallocated memory for the future. + * Stack depot already contains this stack trace, but let's + * keep the preallocated memory for the future. */ depot_init_pool(&prealloc); } @@ -463,7 +467,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, raw_spin_unlock_irqrestore(&pool_lock, flags); exit: if (prealloc) { - /* Nobody used this memory, ok to free it. */ + /* Stack depot didn't use this memory, free it. */ free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER); } if (found) @@ -474,16 +478,16 @@ fast_exit: EXPORT_SYMBOL_GPL(__stack_depot_save); /** - * stack_depot_save - Save a stack trace from an array + * stack_depot_save - Save a stack trace to stack depot * - * @entries: Pointer to storage array - * @nr_entries: Size of the storage array - * @alloc_flags: Allocation gfp flags + * @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: The handle of the stack struct stored in depot, 0 on failure. + * 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, @@ -494,13 +498,12 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries, EXPORT_SYMBOL_GPL(stack_depot_save); /** - * stack_depot_fetch - Fetch stack entries from a depot + * stack_depot_fetch - Fetch a stack trace from stack depot * - * @handle: Stack depot handle which was returned from - * stack_depot_save(). - * @entries: Pointer to store the entries address + * @handle: Stack depot handle returned from stack_depot_save() + * @entries: Pointer to store the address of the stack trace * - * Return: The number of trace entries for this depot. + * Return: Number of frames for the fetched stack */ unsigned int stack_depot_fetch(depot_stack_handle_t handle, unsigned long **entries) @@ -535,11 +538,9 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle, EXPORT_SYMBOL_GPL(stack_depot_fetch); /** - * stack_depot_print - print stack entries from a depot - * - * @stack: Stack depot handle which was returned from - * stack_depot_save(). + * 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) { @@ -553,17 +554,14 @@ void stack_depot_print(depot_stack_handle_t stack) EXPORT_SYMBOL_GPL(stack_depot_print); /** - * stack_depot_snprint - print stack entries from a depot into a buffer + * stack_depot_snprint - Print a stack trace from stack depot into a buffer * - * @handle: Stack depot handle which was returned from - * stack_depot_save(). + * @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. + * Return: Number of bytes printed */ int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size, int spaces)