blob: 0a17883f4b949d8767e317a55095fcb2f1ea8d37 [file] [log] [blame]
Alexander Potapenkocd110162016-03-25 14:22:08 -07001/*
2 * Generic stack depot for storing stack traces.
3 *
4 * Some debugging tools need to save stack traces of certain events which can
5 * be later presented to the user. For example, KASAN needs to safe alloc and
6 * free stacks for each object, but storing two stack traces per object
7 * requires too much memory (e.g. SLUB_DEBUG needs 256 bytes per object for
8 * that).
9 *
10 * Instead, stack depot maintains a hashtable of unique stacktraces. Since alloc
11 * and free stacks repeat a lot, we save about 100x space.
12 * Stacks are never removed from depot, so we store them contiguously one after
13 * another in a contiguos memory allocation.
14 *
15 * Author: Alexander Potapenko <glider@google.com>
16 * Copyright (C) 2016 Google, Inc.
17 *
18 * Based on code by Dmitry Chernenkov.
19 *
20 * This program is free software; you can redistribute it and/or
21 * modify it under the terms of the GNU General Public License
22 * version 2 as published by the Free Software Foundation.
23 *
24 * This program is distributed in the hope that it will be useful, but
25 * WITHOUT ANY WARRANTY; without even the implied warranty of
26 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
27 * General Public License for more details.
28 *
29 */
30
31#include <linux/gfp.h>
32#include <linux/jhash.h>
33#include <linux/kernel.h>
34#include <linux/mm.h>
35#include <linux/percpu.h>
36#include <linux/printk.h>
37#include <linux/slab.h>
38#include <linux/stacktrace.h>
39#include <linux/stackdepot.h>
40#include <linux/string.h>
41#include <linux/types.h>
42
43#define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
44
Joonsoo Kim7c311902016-05-05 16:22:35 -070045#define STACK_ALLOC_NULL_PROTECTION_BITS 1
Alexander Potapenkocd110162016-03-25 14:22:08 -070046#define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */
47#define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER))
48#define STACK_ALLOC_ALIGN 4
49#define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \
50 STACK_ALLOC_ALIGN)
Joonsoo Kim7c311902016-05-05 16:22:35 -070051#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \
52 STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS)
Dmitry Vyukov02754e02016-10-27 17:46:44 -070053#define STACK_ALLOC_SLABS_CAP 8192
Alexander Potapenkocd110162016-03-25 14:22:08 -070054#define STACK_ALLOC_MAX_SLABS \
55 (((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
56 (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP)
57
58/* The compact structure to store the reference to stacks. */
59union handle_parts {
60 depot_stack_handle_t handle;
61 struct {
62 u32 slabindex : STACK_ALLOC_INDEX_BITS;
63 u32 offset : STACK_ALLOC_OFFSET_BITS;
Joonsoo Kim7c311902016-05-05 16:22:35 -070064 u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS;
Alexander Potapenkocd110162016-03-25 14:22:08 -070065 };
66};
67
68struct stack_record {
69 struct stack_record *next; /* Link in the hashtable */
70 u32 hash; /* Hash in the hastable */
71 u32 size; /* Number of frames in the stack */
72 union handle_parts handle;
73 unsigned long entries[1]; /* Variable-sized array of entries. */
74};
75
76static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
77
78static int depot_index;
79static int next_slab_inited;
80static size_t depot_offset;
Zqiange7f7cf92021-05-06 18:03:40 -070081static DEFINE_RAW_SPINLOCK(depot_lock);
Alexander Potapenkocd110162016-03-25 14:22:08 -070082
83static bool init_stack_slab(void **prealloc)
84{
85 if (!*prealloc)
86 return false;
87 /*
88 * This smp_load_acquire() pairs with smp_store_release() to
89 * |next_slab_inited| below and in depot_alloc_stack().
90 */
91 if (smp_load_acquire(&next_slab_inited))
92 return true;
93 if (stack_slabs[depot_index] == NULL) {
94 stack_slabs[depot_index] = *prealloc;
Alexander Potapenko719742a2020-02-20 20:04:30 -080095 *prealloc = NULL;
Alexander Potapenkocd110162016-03-25 14:22:08 -070096 } else {
Alexander Potapenko719742a2020-02-20 20:04:30 -080097 /* If this is the last depot slab, do not touch the next one. */
98 if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) {
99 stack_slabs[depot_index + 1] = *prealloc;
100 *prealloc = NULL;
101 }
Alexander Potapenkocd110162016-03-25 14:22:08 -0700102 /*
103 * This smp_store_release pairs with smp_load_acquire() from
104 * |next_slab_inited| above and in depot_save_stack().
105 */
106 smp_store_release(&next_slab_inited, 1);
107 }
Alexander Potapenkocd110162016-03-25 14:22:08 -0700108 return true;
109}
110
111/* Allocation of a new stack in raw storage */
112static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
113 u32 hash, void **prealloc, gfp_t alloc_flags)
114{
115 int required_size = offsetof(struct stack_record, entries) +
116 sizeof(unsigned long) * size;
117 struct stack_record *stack;
118
119 required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN);
120
121 if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) {
122 if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) {
123 WARN_ONCE(1, "Stack depot reached limit capacity");
124 return NULL;
125 }
126 depot_index++;
127 depot_offset = 0;
128 /*
129 * smp_store_release() here pairs with smp_load_acquire() from
130 * |next_slab_inited| in depot_save_stack() and
131 * init_stack_slab().
132 */
133 if (depot_index + 1 < STACK_ALLOC_MAX_SLABS)
134 smp_store_release(&next_slab_inited, 0);
135 }
136 init_stack_slab(prealloc);
137 if (stack_slabs[depot_index] == NULL)
138 return NULL;
139
140 stack = stack_slabs[depot_index] + depot_offset;
141
142 stack->hash = hash;
143 stack->size = size;
144 stack->handle.slabindex = depot_index;
145 stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
Joonsoo Kim7c311902016-05-05 16:22:35 -0700146 stack->handle.valid = 1;
Alexander Potapenkocd110162016-03-25 14:22:08 -0700147 memcpy(stack->entries, entries, size * sizeof(unsigned long));
148 depot_offset += required_size;
149
150 return stack;
151}
152
153#define STACK_HASH_ORDER 20
154#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
155#define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
156#define STACK_HASH_SEED 0x9747b28c
157
158static struct stack_record *stack_table[STACK_HASH_SIZE] = {
159 [0 ... STACK_HASH_SIZE - 1] = NULL
160};
161
162/* Calculate hash for a stack */
163static inline u32 hash_stack(unsigned long *entries, unsigned int size)
164{
165 return jhash2((u32 *)entries,
166 size * sizeof(unsigned long) / sizeof(u32),
167 STACK_HASH_SEED);
168}
169
170/* Find a stack that is equal to the one stored in entries in the hash */
171static inline struct stack_record *find_stack(struct stack_record *bucket,
172 unsigned long *entries, int size,
173 u32 hash)
174{
175 struct stack_record *found;
176
177 for (found = bucket; found; found = found->next) {
178 if (found->hash == hash &&
179 found->size == size &&
180 !memcmp(entries, found->entries,
181 size * sizeof(unsigned long))) {
182 return found;
183 }
184 }
185 return NULL;
186}
187
188void depot_fetch_stack(depot_stack_handle_t handle, struct stack_trace *trace)
189{
190 union handle_parts parts = { .handle = handle };
191 void *slab = stack_slabs[parts.slabindex];
192 size_t offset = parts.offset << STACK_ALLOC_ALIGN;
193 struct stack_record *stack = slab + offset;
194
195 trace->nr_entries = trace->max_entries = stack->size;
196 trace->entries = stack->entries;
197 trace->skip = 0;
198}
Chris Wilsonae65a212016-11-10 10:46:47 -0800199EXPORT_SYMBOL_GPL(depot_fetch_stack);
Alexander Potapenkocd110162016-03-25 14:22:08 -0700200
201/**
202 * depot_save_stack - save stack in a stack depot.
203 * @trace - the stacktrace to save.
204 * @alloc_flags - flags for allocating additional memory if required.
205 *
206 * Returns the handle of the stack struct stored in depot.
207 */
208depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
209 gfp_t alloc_flags)
210{
211 u32 hash;
212 depot_stack_handle_t retval = 0;
213 struct stack_record *found = NULL, **bucket;
214 unsigned long flags;
215 struct page *page = NULL;
216 void *prealloc = NULL;
217
218 if (unlikely(trace->nr_entries == 0))
219 goto fast_exit;
220
221 hash = hash_stack(trace->entries, trace->nr_entries);
Alexander Potapenkocd110162016-03-25 14:22:08 -0700222 bucket = &stack_table[hash & STACK_HASH_MASK];
223
224 /*
225 * Fast path: look the stack trace up without locking.
226 * The smp_load_acquire() here pairs with smp_store_release() to
227 * |bucket| below.
228 */
229 found = find_stack(smp_load_acquire(bucket), trace->entries,
230 trace->nr_entries, hash);
231 if (found)
232 goto exit;
233
234 /*
235 * Check if the current or the next stack slab need to be initialized.
236 * If so, allocate the memory - we won't be able to do that under the
237 * lock.
238 *
239 * The smp_load_acquire() here pairs with smp_store_release() to
240 * |next_slab_inited| in depot_alloc_stack() and init_stack_slab().
241 */
242 if (unlikely(!smp_load_acquire(&next_slab_inited))) {
243 /*
244 * Zero out zone modifiers, as we don't have specific zone
245 * requirements. Keep the flags related to allocation in atomic
Andrey Ryabinin9485c0d2024-04-18 16:11:33 +0200246 * contexts, I/O, nolockdep.
Alexander Potapenkocd110162016-03-25 14:22:08 -0700247 */
248 alloc_flags &= ~GFP_ZONEMASK;
Andrey Ryabinin9485c0d2024-04-18 16:11:33 +0200249 alloc_flags &= (GFP_ATOMIC | GFP_KERNEL | __GFP_NOLOCKDEP);
Kirill A. Shutemov87cc2712016-07-28 15:49:10 -0700250 alloc_flags |= __GFP_NOWARN;
Alexander Potapenkocd110162016-03-25 14:22:08 -0700251 page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
252 if (page)
253 prealloc = page_address(page);
254 }
255
Zqiange7f7cf92021-05-06 18:03:40 -0700256 raw_spin_lock_irqsave(&depot_lock, flags);
Alexander Potapenkocd110162016-03-25 14:22:08 -0700257
258 found = find_stack(*bucket, trace->entries, trace->nr_entries, hash);
259 if (!found) {
260 struct stack_record *new =
261 depot_alloc_stack(trace->entries, trace->nr_entries,
262 hash, &prealloc, alloc_flags);
263 if (new) {
264 new->next = *bucket;
265 /*
266 * This smp_store_release() pairs with
267 * smp_load_acquire() from |bucket| above.
268 */
269 smp_store_release(bucket, new);
270 found = new;
271 }
272 } else if (prealloc) {
273 /*
274 * We didn't need to store this stack trace, but let's keep
275 * the preallocated memory for the future.
276 */
277 WARN_ON(!init_stack_slab(&prealloc));
278 }
279
Zqiange7f7cf92021-05-06 18:03:40 -0700280 raw_spin_unlock_irqrestore(&depot_lock, flags);
Alexander Potapenkocd110162016-03-25 14:22:08 -0700281exit:
282 if (prealloc) {
283 /* Nobody used this memory, ok to free it. */
284 free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
285 }
286 if (found)
287 retval = found->handle.handle;
288fast_exit:
289 return retval;
290}
Chris Wilsonae65a212016-11-10 10:46:47 -0800291EXPORT_SYMBOL_GPL(depot_save_stack);