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![Alexander Potapenko](/assets/img/avatar_default.png)
stackdepot used to call memcmp(), which compiler tools normally instrument, therefore every lookup used to unnecessarily call instrumented code. This is somewhat ok in the case of KASAN, but under KMSAN a lot of time was spent in the instrumentation. Link: http://lkml.kernel.org/r/20171117172149.69562-1-glider@google.com Signed-off-by: Alexander Potapenko <glider@google.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
300 lines
8.8 KiB
C
300 lines
8.8 KiB
C
/*
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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 contiguos memory allocation.
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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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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* version 2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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*/
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#include <linux/gfp.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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#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[1]; /* 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_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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} else {
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stack_slabs[depot_index + 1] = *prealloc;
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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 depot_save_stack().
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*/
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smp_store_release(&next_slab_inited, 1);
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}
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*prealloc = NULL;
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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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int required_size = offsetof(struct stack_record, entries) +
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sizeof(unsigned long) * size;
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struct stack_record *stack;
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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 depot_save_stack() 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, size * sizeof(unsigned long));
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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_ORDER 20
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#define STACK_HASH_SIZE (1L << 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 struct stack_record *stack_table[STACK_HASH_SIZE] = {
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[0 ... STACK_HASH_SIZE - 1] = NULL
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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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size * sizeof(unsigned long) / sizeof(u32),
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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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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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void depot_fetch_stack(depot_stack_handle_t handle, struct stack_trace *trace)
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{
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union handle_parts parts = { .handle = handle };
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void *slab = stack_slabs[parts.slabindex];
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size_t offset = parts.offset << STACK_ALLOC_ALIGN;
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struct stack_record *stack = slab + offset;
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trace->nr_entries = trace->max_entries = stack->size;
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trace->entries = stack->entries;
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trace->skip = 0;
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}
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EXPORT_SYMBOL_GPL(depot_fetch_stack);
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/**
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* depot_save_stack - save stack in a stack depot.
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* @trace - the stacktrace to save.
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* @alloc_flags - flags for allocating additional memory if required.
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*
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* Returns the handle of the stack struct stored in depot.
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*/
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depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
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gfp_t alloc_flags)
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{
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u32 hash;
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depot_stack_handle_t retval = 0;
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struct stack_record *found = NULL, **bucket;
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unsigned long flags;
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struct page *page = NULL;
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void *prealloc = NULL;
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if (unlikely(trace->nr_entries == 0))
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goto fast_exit;
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hash = hash_stack(trace->entries, trace->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), trace->entries,
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trace->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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spin_lock_irqsave(&depot_lock, flags);
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found = find_stack(*bucket, trace->entries, trace->nr_entries, hash);
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if (!found) {
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struct stack_record *new =
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depot_alloc_stack(trace->entries, trace->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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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(depot_save_stack);
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