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Diffstat (limited to 'lib/stackdepot.c')
| -rw-r--r-- | lib/stackdepot.c | 535 |
1 files changed, 535 insertions, 0 deletions
diff --git a/lib/stackdepot.c b/lib/stackdepot.c new file mode 100644 index 000000000..79e894cf8 --- /dev/null +++ b/lib/stackdepot.c @@ -0,0 +1,535 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Generic stack depot for storing stack traces. + * + * 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). + * + * 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. + * + * Author: Alexander Potapenko <glider@google.com> + * Copyright (C) 2016 Google, Inc. + * + * Based on code by Dmitry Chernenkov. + */ + +#include <linux/gfp.h> +#include <linux/jhash.h> +#include <linux/kernel.h> +#include <linux/mm.h> +#include <linux/mutex.h> +#include <linux/percpu.h> +#include <linux/printk.h> +#include <linux/slab.h> +#include <linux/stacktrace.h> +#include <linux/stackdepot.h> +#include <linux/string.h> +#include <linux/types.h> +#include <linux/memblock.h> +#include <linux/kasan-enabled.h> + +#define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8) + +#define STACK_ALLOC_NULL_PROTECTION_BITS 1 +#define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */ +#define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER)) +#define STACK_ALLOC_ALIGN 4 +#define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \ + STACK_ALLOC_ALIGN) +#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \ + STACK_ALLOC_NULL_PROTECTION_BITS - \ + STACK_ALLOC_OFFSET_BITS - STACK_DEPOT_EXTRA_BITS) +#define STACK_ALLOC_SLABS_CAP 8192 +#define STACK_ALLOC_MAX_SLABS \ + (((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \ + (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP) + +/* The compact structure to store the reference to stacks. */ +union handle_parts { + depot_stack_handle_t handle; + struct { + u32 slabindex : STACK_ALLOC_INDEX_BITS; + u32 offset : STACK_ALLOC_OFFSET_BITS; + u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS; + u32 extra : STACK_DEPOT_EXTRA_BITS; + }; +}; + +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 */ + union handle_parts handle; + unsigned long entries[]; /* Variable-sized array of entries. */ +}; + +static bool __stack_depot_want_early_init __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT); +static bool __stack_depot_early_init_passed __initdata; + +static void *stack_slabs[STACK_ALLOC_MAX_SLABS]; + +static int depot_index; +static int next_slab_inited; +static size_t depot_offset; +static DEFINE_RAW_SPINLOCK(depot_lock); + +unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle) +{ + union handle_parts parts = { .handle = handle }; + + return parts.extra; +} +EXPORT_SYMBOL(stack_depot_get_extra_bits); + +static bool init_stack_slab(void **prealloc) +{ + if (!*prealloc) + return false; + /* + * This smp_load_acquire() pairs with smp_store_release() to + * |next_slab_inited| below and in depot_alloc_stack(). + */ + if (smp_load_acquire(&next_slab_inited)) + return true; + if (stack_slabs[depot_index] == NULL) { + stack_slabs[depot_index] = *prealloc; + *prealloc = NULL; + } else { + /* If this is the last depot slab, do not touch the next one. */ + if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) { + stack_slabs[depot_index + 1] = *prealloc; + *prealloc = NULL; + } + /* + * This smp_store_release pairs with smp_load_acquire() from + * |next_slab_inited| above and in stack_depot_save(). + */ + smp_store_release(&next_slab_inited, 1); + } + return true; +} + +/* Allocation of a new stack in raw storage */ +static struct stack_record * +depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc) +{ + struct stack_record *stack; + size_t required_size = struct_size(stack, entries, size); + + required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN); + + if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) { + if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) { + WARN_ONCE(1, "Stack depot reached limit capacity"); + return NULL; + } + depot_index++; + depot_offset = 0; + /* + * smp_store_release() here pairs with smp_load_acquire() from + * |next_slab_inited| in stack_depot_save() and + * init_stack_slab(). + */ + if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) + smp_store_release(&next_slab_inited, 0); + } + init_stack_slab(prealloc); + if (stack_slabs[depot_index] == NULL) + return NULL; + + stack = stack_slabs[depot_index] + depot_offset; + + stack->hash = hash; + stack->size = size; + stack->handle.slabindex = depot_index; + stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN; + stack->handle.valid = 1; + stack->handle.extra = 0; + memcpy(stack->entries, entries, flex_array_size(stack, entries, size)); + depot_offset += required_size; + + return stack; +} + +/* one hash table bucket entry per 16kB of memory */ +#define STACK_HASH_SCALE 14 +/* limited between 4k and 1M buckets */ +#define STACK_HASH_ORDER_MIN 12 +#define STACK_HASH_ORDER_MAX 20 +#define STACK_HASH_SEED 0x9747b28c + +static unsigned int stack_hash_order; +static unsigned int stack_hash_mask; + +static bool stack_depot_disable; +static struct stack_record **stack_table; + +static int __init is_stack_depot_disabled(char *str) +{ + int ret; + + ret = kstrtobool(str, &stack_depot_disable); + if (!ret && stack_depot_disable) { + pr_info("Stack Depot is disabled\n"); + stack_table = NULL; + } + return 0; +} +early_param("stack_depot_disable", is_stack_depot_disabled); + +void __init stack_depot_want_early_init(void) +{ + /* Too late to request early init now */ + WARN_ON(__stack_depot_early_init_passed); + + __stack_depot_want_early_init = true; +} + +int __init stack_depot_early_init(void) +{ + unsigned long entries = 0; + + /* This is supposed to be called only once, from mm_init() */ + if (WARN_ON(__stack_depot_early_init_passed)) + return 0; + + __stack_depot_early_init_passed = true; + + if (kasan_enabled() && !stack_hash_order) + stack_hash_order = STACK_HASH_ORDER_MAX; + + if (!__stack_depot_want_early_init || stack_depot_disable) + return 0; + + if (stack_hash_order) + entries = 1UL << stack_hash_order; + stack_table = alloc_large_system_hash("stackdepot", + sizeof(struct stack_record *), + entries, + STACK_HASH_SCALE, + HASH_EARLY | HASH_ZERO, + NULL, + &stack_hash_mask, + 1UL << STACK_HASH_ORDER_MIN, + 1UL << STACK_HASH_ORDER_MAX); + + if (!stack_table) { + pr_err("Stack Depot hash table allocation failed, disabling\n"); + stack_depot_disable = true; + return -ENOMEM; + } + + return 0; +} + +int stack_depot_init(void) +{ + static DEFINE_MUTEX(stack_depot_init_mutex); + int ret = 0; + + mutex_lock(&stack_depot_init_mutex); + if (!stack_depot_disable && !stack_table) { + unsigned long entries; + int scale = STACK_HASH_SCALE; + + if (stack_hash_order) { + entries = 1UL << stack_hash_order; + } else { + entries = nr_free_buffer_pages(); + entries = roundup_pow_of_two(entries); + + if (scale > PAGE_SHIFT) + entries >>= (scale - PAGE_SHIFT); + else + entries <<= (PAGE_SHIFT - scale); + } + + if (entries < 1UL << STACK_HASH_ORDER_MIN) + entries = 1UL << STACK_HASH_ORDER_MIN; + if (entries > 1UL << STACK_HASH_ORDER_MAX) + entries = 1UL << STACK_HASH_ORDER_MAX; + + pr_info("Stack Depot allocating hash table of %lu entries with kvcalloc\n", + entries); + stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL); + if (!stack_table) { + pr_err("Stack Depot hash table allocation failed, disabling\n"); + stack_depot_disable = true; + ret = -ENOMEM; + } + stack_hash_mask = entries - 1; + } + mutex_unlock(&stack_depot_init_mutex); + return ret; +} +EXPORT_SYMBOL_GPL(stack_depot_init); + +/* Calculate hash for a stack */ +static inline u32 hash_stack(unsigned long *entries, unsigned int size) +{ + return jhash2((u32 *)entries, + array_size(size, sizeof(*entries)) / sizeof(u32), + STACK_HASH_SEED); +} + +/* Use our own, non-instrumented version of memcmp(). + * + * We actually don't care about the order, just the equality. + */ +static inline +int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, + unsigned int n) +{ + for ( ; n-- ; u1++, u2++) { + if (*u1 != *u2) + return 1; + } + return 0; +} + +/* Find a stack that is equal to the one stored in entries in the hash */ +static inline struct stack_record *find_stack(struct stack_record *bucket, + unsigned long *entries, int size, + u32 hash) +{ + struct stack_record *found; + + for (found = bucket; found; found = found->next) { + if (found->hash == hash && + found->size == size && + !stackdepot_memcmp(entries, found->entries, size)) + return found; + } + return NULL; +} + +/** + * stack_depot_snprint - print stack entries from a depot into a buffer + * + * @handle: Stack depot handle which was 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) +{ + unsigned long *entries; + unsigned int nr_entries; + + nr_entries = stack_depot_fetch(handle, &entries); + return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries, + spaces) : 0; +} +EXPORT_SYMBOL_GPL(stack_depot_snprint); + +/** + * stack_depot_print - print stack entries from a depot + * + * @stack: Stack depot handle which was returned from + * stack_depot_save(). + * + */ +void stack_depot_print(depot_stack_handle_t stack) +{ + unsigned long *entries; + unsigned int nr_entries; + + nr_entries = stack_depot_fetch(stack, &entries); + if (nr_entries > 0) + stack_trace_print(entries, nr_entries, 0); +} +EXPORT_SYMBOL_GPL(stack_depot_print); + +/** + * stack_depot_fetch - Fetch stack entries from a depot + * + * @handle: Stack depot handle which was returned from + * stack_depot_save(). + * @entries: Pointer to store the entries address + * + * Return: The number of trace entries for this depot. + */ +unsigned int stack_depot_fetch(depot_stack_handle_t handle, + unsigned long **entries) +{ + union handle_parts parts = { .handle = handle }; + void *slab; + size_t offset = parts.offset << STACK_ALLOC_ALIGN; + struct stack_record *stack; + + *entries = NULL; + if (!handle) + return 0; + + if (parts.slabindex > depot_index) { + WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n", + parts.slabindex, depot_index, handle); + return 0; + } + slab = stack_slabs[parts.slabindex]; + if (!slab) + return 0; + stack = slab + offset; + + *entries = stack->entries; + return stack->size; +} +EXPORT_SYMBOL_GPL(stack_depot_fetch); + +/** + * __stack_depot_save - Save a stack trace from an array + * + * @entries: Pointer to storage array + * @nr_entries: Size of the storage array + * @extra_bits: Flags to store in unused bits of depot_stack_handle_t + * @alloc_flags: Allocation gfp flags + * @can_alloc: Allocate stack slabs (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 slab pool 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. + * + * If the stack trace in @entries is from an interrupt, only the portion up to + * interrupt entry is saved. + * + * Additional opaque flags can be passed in @extra_bits, stored in the unused + * bits of the stack handle, and retrieved using stack_depot_get_extra_bits() + * without calling stack_depot_fetch(). + * + * 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 + * %GFP_NOWAIT can be used (NMI, raw_spin_lock). + * + * Return: The 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, + unsigned int extra_bits, + gfp_t alloc_flags, bool can_alloc) +{ + struct stack_record *found = NULL, **bucket; + union handle_parts retval = { .handle = 0 }; + struct page *page = NULL; + void *prealloc = NULL; + unsigned long flags; + u32 hash; + + /* + * If this stack trace is from an interrupt, including anything before + * interrupt entry usually leads to unbounded stackdepot 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. + */ + nr_entries = filter_irq_stacks(entries, nr_entries); + + if (unlikely(nr_entries == 0) || stack_depot_disable) + goto fast_exit; + + hash = hash_stack(entries, nr_entries); + bucket = &stack_table[hash & stack_hash_mask]; + + /* + * Fast path: look the stack trace up without locking. + * The smp_load_acquire() here pairs with smp_store_release() to + * |bucket| below. + */ + found = find_stack(smp_load_acquire(bucket), entries, + nr_entries, hash); + if (found) + goto exit; + + /* + * Check if the current or the next stack slab need to be initialized. + * If so, allocate the memory - we won't be able to do that under the + * lock. + * + * The smp_load_acquire() here pairs with smp_store_release() to + * |next_slab_inited| in depot_alloc_stack() and init_stack_slab(). + */ + if (unlikely(can_alloc && !smp_load_acquire(&next_slab_inited))) { + /* + * Zero out zone modifiers, as we don't have specific zone + * requirements. Keep the flags related to allocation in atomic + * contexts and I/O. + */ + alloc_flags &= ~GFP_ZONEMASK; + alloc_flags &= (GFP_ATOMIC | GFP_KERNEL); + alloc_flags |= __GFP_NOWARN; + page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER); + if (page) + prealloc = page_address(page); + } + + raw_spin_lock_irqsave(&depot_lock, flags); + + found = find_stack(*bucket, entries, nr_entries, hash); + if (!found) { + struct stack_record *new = depot_alloc_stack(entries, nr_entries, hash, &prealloc); + + if (new) { + new->next = *bucket; + /* + * This smp_store_release() pairs with + * smp_load_acquire() from |bucket| above. + */ + smp_store_release(bucket, new); + found = new; + } + } else if (prealloc) { + /* + * We didn't need to store this stack trace, but let's keep + * the preallocated memory for the future. + */ + WARN_ON(!init_stack_slab(&prealloc)); + } + + raw_spin_unlock_irqrestore(&depot_lock, flags); +exit: + if (prealloc) { + /* Nobody used this memory, ok to free it. */ + free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER); + } + if (found) + retval.handle = found->handle.handle; +fast_exit: + retval.extra = extra_bits; + + return retval.handle; +} +EXPORT_SYMBOL_GPL(__stack_depot_save); + +/** + * stack_depot_save - Save a stack trace from an array + * + * @entries: Pointer to storage array + * @nr_entries: Size of the storage array + * @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. + */ +depot_stack_handle_t stack_depot_save(unsigned long *entries, + unsigned int nr_entries, + gfp_t alloc_flags) +{ + return __stack_depot_save(entries, nr_entries, 0, alloc_flags, true); +} +EXPORT_SYMBOL_GPL(stack_depot_save); |