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366 lines
10 KiB
366 lines
10 KiB
// 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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* |
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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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* |
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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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* |
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* Author: Alexander Potapenko <[email protected]> |
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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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*/ |
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#include <linux/gfp.h> |
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#include <linux/interrupt.h> |
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#include <linux/jhash.h> |
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#include <linux/kernel.h> |
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#include <linux/mm.h> |
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#include <linux/percpu.h> |
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#include <linux/printk.h> |
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#include <linux/slab.h> |
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#include <linux/stacktrace.h> |
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#include <linux/stackdepot.h> |
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#include <linux/string.h> |
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#include <linux/types.h> |
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#include <linux/memblock.h> |
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#define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8) |
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#define STACK_ALLOC_NULL_PROTECTION_BITS 1 |
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#define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */ |
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#define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER)) |
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#define STACK_ALLOC_ALIGN 4 |
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#define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \ |
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STACK_ALLOC_ALIGN) |
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#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \ |
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STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS) |
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#define STACK_ALLOC_SLABS_CAP 8192 |
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#define STACK_ALLOC_MAX_SLABS \ |
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(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \ |
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(1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP) |
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/* The compact structure to store the reference to stacks. */ |
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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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u32 slabindex : STACK_ALLOC_INDEX_BITS; |
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u32 offset : STACK_ALLOC_OFFSET_BITS; |
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u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS; |
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}; |
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}; |
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struct stack_record { |
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struct stack_record *next; /* Link in the hashtable */ |
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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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union handle_parts handle; |
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unsigned long entries[]; /* Variable-sized array of entries. */ |
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}; |
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static void *stack_slabs[STACK_ALLOC_MAX_SLABS]; |
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static int depot_index; |
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static int next_slab_inited; |
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static size_t depot_offset; |
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static DEFINE_RAW_SPINLOCK(depot_lock); |
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static bool init_stack_slab(void **prealloc) |
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{ |
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if (!*prealloc) |
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return false; |
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/* |
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* This smp_load_acquire() pairs with smp_store_release() to |
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* |next_slab_inited| below and in depot_alloc_stack(). |
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*/ |
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if (smp_load_acquire(&next_slab_inited)) |
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return true; |
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if (stack_slabs[depot_index] == NULL) { |
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stack_slabs[depot_index] = *prealloc; |
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*prealloc = NULL; |
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} else { |
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/* If this is the last depot slab, do not touch the next one. */ |
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if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) { |
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stack_slabs[depot_index + 1] = *prealloc; |
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*prealloc = NULL; |
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} |
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/* |
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* This smp_store_release pairs with smp_load_acquire() from |
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* |next_slab_inited| above and in stack_depot_save(). |
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*/ |
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smp_store_release(&next_slab_inited, 1); |
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} |
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return true; |
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} |
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/* Allocation of a new stack in raw storage */ |
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static struct stack_record *depot_alloc_stack(unsigned long *entries, int size, |
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u32 hash, void **prealloc, gfp_t alloc_flags) |
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{ |
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struct stack_record *stack; |
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size_t required_size = struct_size(stack, entries, size); |
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required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN); |
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if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) { |
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if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) { |
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WARN_ONCE(1, "Stack depot reached limit capacity"); |
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return NULL; |
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} |
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depot_index++; |
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depot_offset = 0; |
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/* |
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* smp_store_release() here pairs with smp_load_acquire() from |
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* |next_slab_inited| in stack_depot_save() and |
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* init_stack_slab(). |
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*/ |
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if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) |
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smp_store_release(&next_slab_inited, 0); |
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} |
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init_stack_slab(prealloc); |
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if (stack_slabs[depot_index] == NULL) |
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return NULL; |
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stack = stack_slabs[depot_index] + depot_offset; |
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stack->hash = hash; |
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stack->size = size; |
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stack->handle.slabindex = depot_index; |
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stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN; |
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stack->handle.valid = 1; |
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memcpy(stack->entries, entries, flex_array_size(stack, entries, size)); |
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depot_offset += required_size; |
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return stack; |
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} |
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#define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER) |
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#define STACK_HASH_MASK (STACK_HASH_SIZE - 1) |
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#define STACK_HASH_SEED 0x9747b28c |
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static bool stack_depot_disable; |
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static struct stack_record **stack_table; |
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static int __init is_stack_depot_disabled(char *str) |
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{ |
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int ret; |
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ret = kstrtobool(str, &stack_depot_disable); |
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if (!ret && stack_depot_disable) { |
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pr_info("Stack Depot is disabled\n"); |
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stack_table = NULL; |
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} |
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return 0; |
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} |
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early_param("stack_depot_disable", is_stack_depot_disabled); |
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int __init stack_depot_init(void) |
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{ |
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if (!stack_depot_disable) { |
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size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *)); |
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int i; |
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stack_table = memblock_alloc(size, size); |
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for (i = 0; i < STACK_HASH_SIZE; i++) |
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stack_table[i] = NULL; |
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} |
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return 0; |
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} |
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/* Calculate 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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array_size(size, sizeof(*entries)) / sizeof(u32), |
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STACK_HASH_SEED); |
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} |
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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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static inline |
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int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, |
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unsigned int n) |
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{ |
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for ( ; n-- ; u1++, u2++) { |
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if (*u1 != *u2) |
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return 1; |
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} |
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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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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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{ |
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struct stack_record *found; |
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for (found = bucket; found; found = found->next) { |
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if (found->hash == hash && |
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found->size == size && |
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!stackdepot_memcmp(entries, found->entries, size)) |
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return found; |
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} |
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return NULL; |
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} |
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/** |
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* stack_depot_fetch - Fetch stack entries from a 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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* |
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* Return: The number of trace entries for this depot. |
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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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{ |
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union handle_parts parts = { .handle = handle }; |
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void *slab; |
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size_t offset = parts.offset << STACK_ALLOC_ALIGN; |
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struct stack_record *stack; |
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*entries = NULL; |
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if (parts.slabindex > depot_index) { |
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WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n", |
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parts.slabindex, depot_index, handle); |
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return 0; |
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} |
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slab = stack_slabs[parts.slabindex]; |
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if (!slab) |
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return 0; |
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stack = slab + offset; |
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*entries = stack->entries; |
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return stack->size; |
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} |
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EXPORT_SYMBOL_GPL(stack_depot_fetch); |
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/** |
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* stack_depot_save - Save a stack trace from an array |
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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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* |
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* Return: The handle of the stack struct stored in depot |
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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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gfp_t alloc_flags) |
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{ |
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struct stack_record *found = NULL, **bucket; |
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depot_stack_handle_t retval = 0; |
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struct page *page = NULL; |
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void *prealloc = NULL; |
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unsigned long flags; |
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u32 hash; |
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if (unlikely(nr_entries == 0) || stack_depot_disable) |
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goto fast_exit; |
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hash = hash_stack(entries, nr_entries); |
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bucket = &stack_table[hash & STACK_HASH_MASK]; |
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/* |
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* Fast path: look the stack trace up without locking. |
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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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if (found) |
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goto exit; |
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/* |
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* Check if the current or the next stack slab need to be initialized. |
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* If so, allocate the memory - we won't be able to do that under the |
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* lock. |
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* |
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* The smp_load_acquire() here pairs with smp_store_release() to |
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* |next_slab_inited| in depot_alloc_stack() and init_stack_slab(). |
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*/ |
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if (unlikely(!smp_load_acquire(&next_slab_inited))) { |
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/* |
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* Zero out zone modifiers, as we don't have specific zone |
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* requirements. Keep the flags related to allocation in atomic |
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* contexts and I/O. |
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*/ |
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alloc_flags &= ~GFP_ZONEMASK; |
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alloc_flags &= (GFP_ATOMIC | GFP_KERNEL); |
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alloc_flags |= __GFP_NOWARN; |
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page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER); |
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if (page) |
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prealloc = page_address(page); |
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} |
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raw_spin_lock_irqsave(&depot_lock, flags); |
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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 = |
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depot_alloc_stack(entries, nr_entries, |
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hash, &prealloc, alloc_flags); |
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if (new) { |
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new->next = *bucket; |
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/* |
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* This smp_store_release() pairs with |
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* smp_load_acquire() from |bucket| above. |
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*/ |
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smp_store_release(bucket, new); |
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found = new; |
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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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*/ |
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WARN_ON(!init_stack_slab(&prealloc)); |
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} |
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raw_spin_unlock_irqrestore(&depot_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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free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER); |
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} |
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if (found) |
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retval = found->handle.handle; |
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fast_exit: |
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return retval; |
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} |
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EXPORT_SYMBOL_GPL(stack_depot_save); |
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static inline int in_irqentry_text(unsigned long ptr) |
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{ |
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return (ptr >= (unsigned long)&__irqentry_text_start && |
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ptr < (unsigned long)&__irqentry_text_end) || |
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(ptr >= (unsigned long)&__softirqentry_text_start && |
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ptr < (unsigned long)&__softirqentry_text_end); |
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} |
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unsigned int filter_irq_stacks(unsigned long *entries, |
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unsigned int nr_entries) |
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{ |
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unsigned int i; |
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for (i = 0; i < nr_entries; i++) { |
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if (in_irqentry_text(entries[i])) { |
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/* Include the irqentry function into the stack. */ |
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return i + 1; |
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} |
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} |
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return nr_entries; |
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} |
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EXPORT_SYMBOL_GPL(filter_irq_stacks);
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