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Diffstat (limited to 'lib/stackdepot.c')
| -rw-r--r-- | lib/stackdepot.c | 342 |
1 files changed, 342 insertions, 0 deletions
diff --git a/lib/stackdepot.c b/lib/stackdepot.c new file mode 100644 index 000000000..25bbac466 --- /dev/null +++ b/lib/stackdepot.c @@ -0,0 +1,342 @@ +// 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 contiguos 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/interrupt.h> +#include <linux/jhash.h> +#include <linux/kernel.h> +#include <linux/mm.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> + +#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) +#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; + }; +}; + +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[1]; /* Variable-sized array of entries. */ +}; + +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); + +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, gfp_t alloc_flags) +{ + int required_size = offsetof(struct stack_record, entries) + + sizeof(unsigned long) * size; + struct stack_record *stack; + + 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; + memcpy(stack->entries, entries, size * sizeof(unsigned long)); + depot_offset += required_size; + + return stack; +} + +#define STACK_HASH_ORDER 20 +#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER) +#define STACK_HASH_MASK (STACK_HASH_SIZE - 1) +#define STACK_HASH_SEED 0x9747b28c + +static struct stack_record *stack_table[STACK_HASH_SIZE] = { + [0 ... STACK_HASH_SIZE - 1] = NULL +}; + +/* Calculate hash for a stack */ +static inline u32 hash_stack(unsigned long *entries, unsigned int size) +{ + return jhash2((u32 *)entries, + size * sizeof(unsigned long) / 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_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 (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 + * @alloc_flags: Allocation gfp flags + * + * Return: The handle of the stack struct stored in depot + */ +depot_stack_handle_t stack_depot_save(unsigned long *entries, + unsigned int nr_entries, + gfp_t alloc_flags) +{ + struct stack_record *found = NULL, **bucket; + depot_stack_handle_t retval = 0; + struct page *page = NULL; + void *prealloc = NULL; + unsigned long flags; + u32 hash; + + if (unlikely(nr_entries == 0)) + 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(!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, alloc_flags); + 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 = found->handle.handle; +fast_exit: + return retval; +} +EXPORT_SYMBOL_GPL(stack_depot_save); + +static inline int in_irqentry_text(unsigned long ptr) +{ + return (ptr >= (unsigned long)&__irqentry_text_start && + ptr < (unsigned long)&__irqentry_text_end) || + (ptr >= (unsigned long)&__softirqentry_text_start && + ptr < (unsigned long)&__softirqentry_text_end); +} + +unsigned int filter_irq_stacks(unsigned long *entries, + unsigned int nr_entries) +{ + unsigned int i; + + for (i = 0; i < nr_entries; i++) { + if (in_irqentry_text(entries[i])) { + /* Include the irqentry function into the stack. */ + return i + 1; + } + } + return nr_entries; +} +EXPORT_SYMBOL_GPL(filter_irq_stacks); |