[linux-2.6-block.git] / lib / stackdepot.c

/*
 * Generic stack depot for storing stack traces.
 *
 * Some debugging tools need to save stack traces of certain events which can
 * be later presented to the user. For example, KASAN needs to safe alloc and
 * free stacks for each object, but storing two stack traces per object
 * requires too much memory (e.g. SLUB_DEBUG needs 256 bytes per object for
 * that).
 *
 * Instead, stack depot maintains a hashtable of unique stacktraces. Since alloc
 * and free stacks repeat a lot, we save about 100x space.
 * Stacks are never removed from depot, so we store them contiguously one after
 * another in a contiguos memory allocation.
 *
 * Author: Alexander Potapenko <glider@google.com>
 * Copyright (C) 2016 Google, Inc.
 *
 * Based on code by Dmitry Chernenkov.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 */

#include <linux/gfp.h>
#include <linux/jhash.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/stacktrace.h>
#include <linux/stackdepot.h>
#include <linux/string.h>
#include <linux/types.h>

#define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)

#define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */
#define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER))
#define STACK_ALLOC_ALIGN 4
#define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \
					STACK_ALLOC_ALIGN)
#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - STACK_ALLOC_OFFSET_BITS)
#define STACK_ALLOC_SLABS_CAP 1024
#define STACK_ALLOC_MAX_SLABS \
	(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
	 (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP)

/* The compact structure to store the reference to stacks. */
union handle_parts {
	depot_stack_handle_t handle;
	struct {
		u32 slabindex : STACK_ALLOC_INDEX_BITS;
		u32 offset : STACK_ALLOC_OFFSET_BITS;
	};
};

struct stack_record {
	struct stack_record *next;	/* Link in the hashtable */
	u32 hash;			/* Hash in the hastable */
	u32 size;			/* Number of frames in the stack */
	union handle_parts handle;
	unsigned long entries[1];	/* Variable-sized array of entries. */
};

static void *stack_slabs[STACK_ALLOC_MAX_SLABS];

static int depot_index;
static int next_slab_inited;
static size_t depot_offset;
static DEFINE_SPINLOCK(depot_lock);

static bool init_stack_slab(void **prealloc)
{
	if (!*prealloc)
		return false;
	/*
	 * This smp_load_acquire() pairs with smp_store_release() to
	 * |next_slab_inited| below and in depot_alloc_stack().
	 */
	if (smp_load_acquire(&next_slab_inited))
		return true;
	if (stack_slabs[depot_index] == NULL) {
		stack_slabs[depot_index] = *prealloc;
	} else {
		stack_slabs[depot_index + 1] = *prealloc;
		/*
		 * This smp_store_release pairs with smp_load_acquire() from
		 * |next_slab_inited| above and in depot_save_stack().
		 */
		smp_store_release(&next_slab_inited, 1);
	}
	*prealloc = NULL;
	return true;
}

/* Allocation of a new stack in raw storage */
static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
		u32 hash, void **prealloc, gfp_t alloc_flags)
{
	int required_size = offsetof(struct stack_record, entries) +
		sizeof(unsigned long) * size;
	struct stack_record *stack;

	required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN);

	if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) {
		if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) {
			WARN_ONCE(1, "Stack depot reached limit capacity");
			return NULL;
		}
		depot_index++;
		depot_offset = 0;
		/*
		 * smp_store_release() here pairs with smp_load_acquire() from
		 * |next_slab_inited| in depot_save_stack() and
		 * init_stack_slab().
		 */
		if (depot_index + 1 < STACK_ALLOC_MAX_SLABS)
			smp_store_release(&next_slab_inited, 0);
	}
	init_stack_slab(prealloc);
	if (stack_slabs[depot_index] == NULL)
		return NULL;

	stack = stack_slabs[depot_index] + depot_offset;

	stack->hash = hash;
	stack->size = size;
	stack->handle.slabindex = depot_index;
	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
	memcpy(stack->entries, entries, size * sizeof(unsigned long));
	depot_offset += required_size;

	return stack;
}

#define STACK_HASH_ORDER 20
#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
#define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
#define STACK_HASH_SEED 0x9747b28c

static struct stack_record *stack_table[STACK_HASH_SIZE] = {
	[0 ...	STACK_HASH_SIZE - 1] = NULL
};

/* Calculate hash for a stack */
static inline u32 hash_stack(unsigned long *entries, unsigned int size)
{
	return jhash2((u32 *)entries,
			       size * sizeof(unsigned long) / sizeof(u32),
			       STACK_HASH_SEED);
}

/* Find a stack that is equal to the one stored in entries in the hash */
static inline struct stack_record *find_stack(struct stack_record *bucket,
					     unsigned long *entries, int size,
					     u32 hash)
{
	struct stack_record *found;

	for (found = bucket; found; found = found->next) {
		if (found->hash == hash &&
		    found->size == size &&
		    !memcmp(entries, found->entries,
			    size * sizeof(unsigned long))) {
			return found;
		}
	}
	return NULL;
}

void depot_fetch_stack(depot_stack_handle_t handle, struct stack_trace *trace)
{
	union handle_parts parts = { .handle = handle };
	void *slab = stack_slabs[parts.slabindex];
	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
	struct stack_record *stack = slab + offset;

	trace->nr_entries = trace->max_entries = stack->size;
	trace->entries = stack->entries;
	trace->skip = 0;
}

/**
 * depot_save_stack - save stack in a stack depot.
 * @trace - the stacktrace to save.
 * @alloc_flags - flags for allocating additional memory if required.
 *
 * Returns the handle of the stack struct stored in depot.
 */
depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
				    gfp_t alloc_flags)
{
	u32 hash;
	depot_stack_handle_t retval = 0;
	struct stack_record *found = NULL, **bucket;
	unsigned long flags;
	struct page *page = NULL;
	void *prealloc = NULL;

	if (unlikely(trace->nr_entries == 0))
		goto fast_exit;

	hash = hash_stack(trace->entries, trace->nr_entries);
	/* Bad luck, we won't store this stack. */
	if (hash == 0)
		goto exit;

	bucket = &stack_table[hash & STACK_HASH_MASK];

	/*
	 * Fast path: look the stack trace up without locking.
	 * The smp_load_acquire() here pairs with smp_store_release() to
	 * |bucket| below.
	 */
	found = find_stack(smp_load_acquire(bucket), trace->entries,
			   trace->nr_entries, hash);
	if (found)
		goto exit;

	/*
	 * Check if the current or the next stack slab need to be initialized.
	 * If so, allocate the memory - we won't be able to do that under the
	 * lock.
	 *
	 * The smp_load_acquire() here pairs with smp_store_release() to
	 * |next_slab_inited| in depot_alloc_stack() and init_stack_slab().
	 */
	if (unlikely(!smp_load_acquire(&next_slab_inited))) {
		/*
		 * Zero out zone modifiers, as we don't have specific zone
		 * requirements. Keep the flags related to allocation in atomic
		 * contexts and I/O.
		 */
		alloc_flags &= ~GFP_ZONEMASK;
		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
		page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
		if (page)
			prealloc = page_address(page);
	}

	spin_lock_irqsave(&depot_lock, flags);

	found = find_stack(*bucket, trace->entries, trace->nr_entries, hash);
	if (!found) {
		struct stack_record *new =
			depot_alloc_stack(trace->entries, trace->nr_entries,
					  hash, &prealloc, alloc_flags);
		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));
	}

	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;
}
Commit	Line	Data
cd11016e AP	1	/*
	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
	45	#define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */
	46	#define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER))
	47	#define STACK_ALLOC_ALIGN 4
	48	#define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \
	49	STACK_ALLOC_ALIGN)
	50	#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - STACK_ALLOC_OFFSET_BITS)
	51	#define STACK_ALLOC_SLABS_CAP 1024
	52	#define STACK_ALLOC_MAX_SLABS \
	53	(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
	54	(1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP)
	55
	56	/* The compact structure to store the reference to stacks. */
	57	union handle_parts {
	58	depot_stack_handle_t handle;
	59	struct {
	60	u32 slabindex : STACK_ALLOC_INDEX_BITS;
	61	u32 offset : STACK_ALLOC_OFFSET_BITS;
	62	};
	63	};
	64
65	struct stack_record {
66	struct stack_record next; / Link in the hashtable */
67	u32 hash; /* Hash in the hastable */
68	u32 size; /* Number of frames in the stack */
69	union handle_parts handle;
70	unsigned long entries[1]; /* Variable-sized array of entries. */
71	};
72
73	static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
74
75	static int depot_index;
76	static int next_slab_inited;
77	static size_t depot_offset;
78	static DEFINE_SPINLOCK(depot_lock);
79
80	static bool init_stack_slab(void **prealloc)
81	{
82	if (!*prealloc)
83	return false;
84	/*
85	* This smp_load_acquire() pairs with smp_store_release() to
86	* \|next_slab_inited\| below and in depot_alloc_stack().
87	*/
88	if (smp_load_acquire(&next_slab_inited))
89	return true;
90	if (stack_slabs[depot_index] == NULL) {
91	stack_slabs[depot_index] = *prealloc;
92	} else {
93	stack_slabs[depot_index + 1] = *prealloc;
94	/*
95	* This smp_store_release pairs with smp_load_acquire() from
96	* \|next_slab_inited\| above and in depot_save_stack().
97	*/
98	smp_store_release(&next_slab_inited, 1);
99	}
100	*prealloc = NULL;
101	return true;
102	}
103
104	/* Allocation of a new stack in raw storage */
105	static struct stack_record depot_alloc_stack(unsigned long entries, int size,
106	u32 hash, void **prealloc, gfp_t alloc_flags)
107	{
108	int required_size = offsetof(struct stack_record, entries) +
109	sizeof(unsigned long) * size;
110	struct stack_record *stack;
111
112	required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN);
113
114	if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) {
115	if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) {
116	WARN_ONCE(1, "Stack depot reached limit capacity");
117	return NULL;
118	}
119	depot_index++;
120	depot_offset = 0;
121	/*
122	* smp_store_release() here pairs with smp_load_acquire() from
123	* \|next_slab_inited\| in depot_save_stack() and
124	* init_stack_slab().
125	*/
126	if (depot_index + 1 < STACK_ALLOC_MAX_SLABS)
127	smp_store_release(&next_slab_inited, 0);
128	}
129	init_stack_slab(prealloc);
130	if (stack_slabs[depot_index] == NULL)
131	return NULL;
132
133	stack = stack_slabs[depot_index] + depot_offset;
134
135	stack->hash = hash;
136	stack->size = size;
137	stack->handle.slabindex = depot_index;
138	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
139	memcpy(stack->entries, entries, size * sizeof(unsigned long));
140	depot_offset += required_size;
141
142	return stack;
143	}
144
145	#define STACK_HASH_ORDER 20
146	#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
147	#define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
148	#define STACK_HASH_SEED 0x9747b28c
149
150	static struct stack_record *stack_table[STACK_HASH_SIZE] = {
151	[0 ... STACK_HASH_SIZE - 1] = NULL
152	};
153
154	/* Calculate hash for a stack */
155	static inline u32 hash_stack(unsigned long *entries, unsigned int size)
156	{
157	return jhash2((u32 *)entries,
158	size * sizeof(unsigned long) / sizeof(u32),
159	STACK_HASH_SEED);
160	}
161
162	/* Find a stack that is equal to the one stored in entries in the hash */
163	static inline struct stack_record find_stack(struct stack_record bucket,
164	unsigned long *entries, int size,
165	u32 hash)
166	{
167	struct stack_record *found;
168
169	for (found = bucket; found; found = found->next) {
170	if (found->hash == hash &&
171	found->size == size &&
172	!memcmp(entries, found->entries,
173	size * sizeof(unsigned long))) {
174	return found;
175	}
176	}
177	return NULL;
178	}
179
180	void depot_fetch_stack(depot_stack_handle_t handle, struct stack_trace *trace)
181	{
182	union handle_parts parts = { .handle = handle };
183	void *slab = stack_slabs[parts.slabindex];
184	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
185	struct stack_record *stack = slab + offset;
186
187	trace->nr_entries = trace->max_entries = stack->size;
188	trace->entries = stack->entries;
189	trace->skip = 0;
190	}
191
192	/**
193	* depot_save_stack - save stack in a stack depot.
194	* @trace - the stacktrace to save.
195	* @alloc_flags - flags for allocating additional memory if required.
196	*
197	* Returns the handle of the stack struct stored in depot.
198	*/
199	depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
200	gfp_t alloc_flags)
201	{
202	u32 hash;
203	depot_stack_handle_t retval = 0;
204	struct stack_record found = NULL, *bucket;
205	unsigned long flags;
206	struct page *page = NULL;
207	void *prealloc = NULL;
208
209	if (unlikely(trace->nr_entries == 0))
210	goto fast_exit;
211
212	hash = hash_stack(trace->entries, trace->nr_entries);
213	/* Bad luck, we won't store this stack. */
214	if (hash == 0)
215	goto exit;
216
217	bucket = &stack_table[hash & STACK_HASH_MASK];
218
219	/*
220	* Fast path: look the stack trace up without locking.
221	* The smp_load_acquire() here pairs with smp_store_release() to
222	* \|bucket\| below.
223	*/
224	found = find_stack(smp_load_acquire(bucket), trace->entries,
225	trace->nr_entries, hash);
226	if (found)
227	goto exit;
228
229	/*
230	* Check if the current or the next stack slab need to be initialized.
231	* If so, allocate the memory - we won't be able to do that under the
232	* lock.
233	*
234	* The smp_load_acquire() here pairs with smp_store_release() to
235	* \|next_slab_inited\| in depot_alloc_stack() and init_stack_slab().
236	*/
237	if (unlikely(!smp_load_acquire(&next_slab_inited))) {
238	/*
239	* Zero out zone modifiers, as we don't have specific zone
240	* requirements. Keep the flags related to allocation in atomic
241	* contexts and I/O.
242	*/
243	alloc_flags &= ~GFP_ZONEMASK;
244	alloc_flags &= (GFP_ATOMIC \| GFP_KERNEL);
245	page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
246	if (page)
247	prealloc = page_address(page);
248	}
249
250	spin_lock_irqsave(&depot_lock, flags);
251
252	found = find_stack(*bucket, trace->entries, trace->nr_entries, hash);
253	if (!found) {
254	struct stack_record *new =
255	depot_alloc_stack(trace->entries, trace->nr_entries,
256	hash, &prealloc, alloc_flags);
257	if (new) {
258	new->next = *bucket;
259	/*
260	* This smp_store_release() pairs with
261	* smp_load_acquire() from \|bucket\| above.
262	*/
263	smp_store_release(bucket, new);
264	found = new;
265	}
266	} else if (prealloc) {
267	/*
268	* We didn't need to store this stack trace, but let's keep
269	* the preallocated memory for the future.
270	*/
271	WARN_ON(!init_stack_slab(&prealloc));
272	}
273
274	spin_unlock_irqrestore(&depot_lock, flags);
275	exit:
276	if (prealloc) {
277	/* Nobody used this memory, ok to free it. */
278	free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
279	}
280	if (found)
281	retval = found->handle.handle;
282	fast_exit:
283	return retval;
284	}