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![Vlastimil Babka](/assets/img/avatar_default.png)
In a later patch we want to add stackdepot support for object owner tracking in slub caches, which is enabled by slub_debug boot parameter. This creates a bootstrap problem as some caches are created early in boot when slab_is_available() is false and thus stack_depot_init() tries to use memblock. But, as reported by Hyeonggon Yoo [1] we are already beyond memblock_free_all(). Ideally memblock allocation should fail, yet it succeeds, but later the system crashes, which is a separately handled issue. To resolve this boostrap issue in a robust way, this patch adds another way to request stack_depot_early_init(), which happens at a well-defined point of time. In addition to build-time CONFIG_STACKDEPOT_ALWAYS_INIT, code that's e.g. processing boot parameters (which happens early enough) can call a new function stack_depot_want_early_init(), which sets a flag that stack_depot_early_init() will check. In this patch we also convert page_owner to this approach. While it doesn't have the bootstrap issue as slub, it's also a functionality enabled by a boot param and can thus request stack_depot_early_init() with memblock allocation instead of later initialization with kvmalloc(). As suggested by Mike, make stack_depot_early_init() only attempt memblock allocation and stack_depot_init() only attempt kvmalloc(). Also change the latter to kvcalloc(). In both cases we can lose the explicit array zeroing, which the allocations do already. As suggested by Marco, provide empty implementations of the init functions for !CONFIG_STACKDEPOT builds to simplify the callers. [1] https://lore.kernel.org/all/YhnUcqyeMgCrWZbd@ip-172-31-19-208.ap-northeast-1.compute.internal/ Reported-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Suggested-by: Mike Rapoport <rppt@linux.ibm.com> Suggested-by: Marco Elver <elver@google.com> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Marco Elver <elver@google.com> Reviewed-and-tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: David Rientjes <rientjes@google.com>
477 lines
14 KiB
C
477 lines
14 KiB
C
// 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 <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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#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/mutex.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 bool __stack_depot_want_early_init __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
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static bool __stack_depot_early_init_passed __initdata;
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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 *
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depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
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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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void __init stack_depot_want_early_init(void)
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{
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/* Too late to request early init now */
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WARN_ON(__stack_depot_early_init_passed);
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__stack_depot_want_early_init = true;
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}
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int __init stack_depot_early_init(void)
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{
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size_t size;
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/* This is supposed to be called only once, from mm_init() */
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if (WARN_ON(__stack_depot_early_init_passed))
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return 0;
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__stack_depot_early_init_passed = true;
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if (!__stack_depot_want_early_init || stack_depot_disable)
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return 0;
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size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
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pr_info("Stack Depot early init allocating hash table with memblock_alloc, %zu bytes\n",
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size);
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stack_table = memblock_alloc(size, SMP_CACHE_BYTES);
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if (!stack_table) {
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pr_err("Stack Depot hash table allocation failed, disabling\n");
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stack_depot_disable = true;
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return -ENOMEM;
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}
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return 0;
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}
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int stack_depot_init(void)
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{
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static DEFINE_MUTEX(stack_depot_init_mutex);
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int ret = 0;
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mutex_lock(&stack_depot_init_mutex);
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if (!stack_depot_disable && !stack_table) {
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pr_info("Stack Depot allocating hash table with kvcalloc\n");
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stack_table = kvcalloc(STACK_HASH_SIZE, sizeof(struct stack_record *), GFP_KERNEL);
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if (!stack_table) {
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pr_err("Stack Depot hash table allocation failed, disabling\n");
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stack_depot_disable = true;
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ret = -ENOMEM;
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}
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}
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mutex_unlock(&stack_depot_init_mutex);
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return ret;
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}
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EXPORT_SYMBOL_GPL(stack_depot_init);
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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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/* 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_snprint - print stack entries from a depot into a buffer
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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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* @buf: Pointer to the print buffer
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*
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* @size: Size of the print buffer
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*
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* @spaces: Number of leading spaces to print
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*
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* Return: Number of bytes printed.
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*/
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int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
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int spaces)
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{
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unsigned long *entries;
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unsigned int nr_entries;
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nr_entries = stack_depot_fetch(handle, &entries);
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return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
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spaces) : 0;
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}
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EXPORT_SYMBOL_GPL(stack_depot_snprint);
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/**
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* stack_depot_print - print stack entries from a depot
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*
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* @stack: Stack depot handle which was returned from
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* stack_depot_save().
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*
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*/
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void stack_depot_print(depot_stack_handle_t stack)
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{
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unsigned long *entries;
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unsigned int nr_entries;
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nr_entries = stack_depot_fetch(stack, &entries);
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if (nr_entries > 0)
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stack_trace_print(entries, nr_entries, 0);
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}
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EXPORT_SYMBOL_GPL(stack_depot_print);
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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 (!handle)
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return 0;
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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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* @can_alloc: Allocate stack slabs (increased chance of failure if false)
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*
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* Saves a stack trace from @entries array of size @nr_entries. If @can_alloc is
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* %true, is allowed to replenish the stack slab pool in case no space is left
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* (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids
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* any allocations and will fail if no space is left to store the stack trace.
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*
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* If the stack trace in @entries is from an interrupt, only the portion up to
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* interrupt entry is saved.
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*
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* Context: Any context, but setting @can_alloc to %false is required if
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* alloc_pages() cannot be used from the current context. Currently
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* this is the case from contexts where neither %GFP_ATOMIC nor
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* %GFP_NOWAIT can be used (NMI, raw_spin_lock).
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*
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* Return: The handle of the stack struct stored in depot, 0 on failure.
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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, bool can_alloc)
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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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/*
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* If this stack trace is from an interrupt, including anything before
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* interrupt entry usually leads to unbounded stackdepot growth.
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*
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* Because use of filter_irq_stacks() is a requirement to ensure
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* stackdepot can efficiently deduplicate interrupt stacks, always
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* filter_irq_stacks() to simplify all callers' use of stackdepot.
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*/
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nr_entries = filter_irq_stacks(entries, nr_entries);
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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(can_alloc && !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 = depot_alloc_stack(entries, nr_entries, hash, &prealloc);
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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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/**
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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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* Context: Contexts where allocations via alloc_pages() are allowed.
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* See __stack_depot_save() for more details.
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*
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* Return: The handle of the stack struct stored in depot, 0 on failure.
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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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return __stack_depot_save(entries, nr_entries, alloc_flags, true);
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}
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EXPORT_SYMBOL_GPL(stack_depot_save);
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