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![Vlastimil Babka](/assets/img/avatar_default.png)
As Linus explained [1], setting the stackdepot hash table size as a config option is suboptimal, especially as stackdepot becomes a dependency of less "expert" subsystems than initially (e.g. DRM, networking, SLUB_DEBUG): : (a) it introduces a new compile-time question that isn't sane to ask : a regular user, but is now exposed to regular users. : (b) this by default uses 1MB of memory for a feature that didn't in : the past, so now if you have small machines you need to make sure you : make a special kernel config for them. Ideally we would employ rhashtable for fully automatic resizing, which should be feasible for many of the new users, but problematic for the original users with restricted context that call __stack_depot_save() with can_alloc == false, i.e. KASAN. However we can easily remove the config option and scale the hash table automatically with system memory. The STACK_HASH_MASK constant becomes stack_hash_mask variable and is used only in one mask operation, so the overhead should be negligible to none. For early allocation we can employ the existing alloc_large_system_hash() function and perform similar scaling for the late allocation. The existing limits of the config option (between 4k and 1M buckets) are preserved, and scaling factor is set to one bucket per 16kB memory so on 64bit the max 1M buckets (8MB memory) is achieved with 16GB system, while a 1GB system will use 512kB. Because KASAN is reported to need the maximum number of buckets even with smaller amounts of memory [2], set it as such when kasan_enabled(). If needed, the automatic scaling could be complemented with a boot-time kernel parameter, but it feels pointless to add it without a specific use case. [1] https://lore.kernel.org/all/CAHk-=wjC5nS+fnf6EzRD9yQRJApAhxx7gRB87ZV+pAWo9oVrTg@mail.gmail.com/ [2] https://lore.kernel.org/all/CACT4Y+Y4GZfXOru2z5tFPzFdaSUd+GFc6KVL=bsa0+1m197cQQ@mail.gmail.com/ Link: https://lkml.kernel.org/r/20220620150249.16814-1-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Dmitry Vyukov <dvyukov@google.com> Cc: Marco Elver <elver@google.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Konovalov <andreyknvl@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
516 lines
14 KiB
C
516 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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#include <linux/kasan-enabled.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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/* one hash table bucket entry per 16kB of memory */
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#define STACK_HASH_SCALE 14
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/* limited between 4k and 1M buckets */
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#define STACK_HASH_ORDER_MIN 12
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#define STACK_HASH_ORDER_MAX 20
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#define STACK_HASH_SEED 0x9747b28c
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static unsigned int stack_hash_order;
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static unsigned int stack_hash_mask;
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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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unsigned long entries = 0;
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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 (kasan_enabled() && !stack_hash_order)
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stack_hash_order = STACK_HASH_ORDER_MAX;
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if (!__stack_depot_want_early_init || stack_depot_disable)
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return 0;
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if (stack_hash_order)
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entries = 1UL << stack_hash_order;
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stack_table = alloc_large_system_hash("stackdepot",
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sizeof(struct stack_record *),
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entries,
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STACK_HASH_SCALE,
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HASH_EARLY | HASH_ZERO,
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NULL,
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&stack_hash_mask,
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1UL << STACK_HASH_ORDER_MIN,
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1UL << STACK_HASH_ORDER_MAX);
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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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unsigned long entries;
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int scale = STACK_HASH_SCALE;
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if (stack_hash_order) {
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entries = 1UL << stack_hash_order;
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} else {
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entries = nr_free_buffer_pages();
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entries = roundup_pow_of_two(entries);
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if (scale > PAGE_SHIFT)
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entries >>= (scale - PAGE_SHIFT);
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else
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entries <<= (PAGE_SHIFT - scale);
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}
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if (entries < 1UL << STACK_HASH_ORDER_MIN)
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entries = 1UL << STACK_HASH_ORDER_MIN;
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if (entries > 1UL << STACK_HASH_ORDER_MAX)
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entries = 1UL << STACK_HASH_ORDER_MAX;
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pr_info("Stack Depot allocating hash table of %lu entries with kvcalloc\n",
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entries);
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stack_table = kvcalloc(entries, 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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stack_hash_mask = entries - 1;
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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);
|
|
alloc_flags |= __GFP_NOWARN;
|
|
page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
|
|
if (page)
|
|
prealloc = page_address(page);
|
|
}
|
|
|
|
raw_spin_lock_irqsave(&depot_lock, flags);
|
|
|
|
found = find_stack(*bucket, entries, nr_entries, hash);
|
|
if (!found) {
|
|
struct stack_record *new = depot_alloc_stack(entries, nr_entries, hash, &prealloc);
|
|
|
|
if (new) {
|
|
new->next = *bucket;
|
|
/*
|
|
* This smp_store_release() pairs with
|
|
* smp_load_acquire() from |bucket| above.
|
|
*/
|
|
smp_store_release(bucket, new);
|
|
found = new;
|
|
}
|
|
} else if (prealloc) {
|
|
/*
|
|
* We didn't need to store this stack trace, but let's keep
|
|
* the preallocated memory for the future.
|
|
*/
|
|
WARN_ON(!init_stack_slab(&prealloc));
|
|
}
|
|
|
|
raw_spin_unlock_irqrestore(&depot_lock, flags);
|
|
exit:
|
|
if (prealloc) {
|
|
/* Nobody used this memory, ok to free it. */
|
|
free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
|
|
}
|
|
if (found)
|
|
retval = found->handle.handle;
|
|
fast_exit:
|
|
return retval;
|
|
}
|
|
EXPORT_SYMBOL_GPL(__stack_depot_save);
|
|
|
|
/**
|
|
* stack_depot_save - Save a stack trace from an array
|
|
*
|
|
* @entries: Pointer to storage array
|
|
* @nr_entries: Size of the storage array
|
|
* @alloc_flags: Allocation gfp flags
|
|
*
|
|
* Context: Contexts where allocations via alloc_pages() are allowed.
|
|
* See __stack_depot_save() for more details.
|
|
*
|
|
* Return: The handle of the stack struct stored in depot, 0 on failure.
|
|
*/
|
|
depot_stack_handle_t stack_depot_save(unsigned long *entries,
|
|
unsigned int nr_entries,
|
|
gfp_t alloc_flags)
|
|
{
|
|
return __stack_depot_save(entries, nr_entries, alloc_flags, true);
|
|
}
|
|
EXPORT_SYMBOL_GPL(stack_depot_save);
|