lib/stackdepot.c - kernel/msm-4.9 - Gitiles

 /*
  * 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_NULL_PROTECTION_BITS 1
 #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_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS)
 #define STACK_ALLOC_SLABS_CAP 8192
 #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;
 		u32 valid : STACK_ALLOC_NULL_PROTECTION_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;
 		*prealloc = NULL;
 	} else {
 		/* If this is the last depot slab, do not touch the next one. */
 		if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) {
 			stack_slabs[depot_index + 1] = *prealloc;
 			*prealloc = NULL;
 		}
 		/*
 		 * 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);
 	}
 	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;
 	stack->handle.valid = 1;
 	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;
 }
 EXPORT_SYMBOL_GPL(depot_fetch_stack);

 /**
  * 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);
 	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);
 		alloc_flags |= __GFP_NOWARN;
 		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;
 }
 EXPORT_SYMBOL_GPL(depot_save_stack);
	/*
	* 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_NULL_PROTECTION_BITS 1
	#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_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS)
	#define STACK_ALLOC_SLABS_CAP 8192
	#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;
	u32 valid : STACK_ALLOC_NULL_PROTECTION_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;
	*prealloc = NULL;
	} else {
	/* If this is the last depot slab, do not touch the next one. */
	if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) {
	stack_slabs[depot_index + 1] = *prealloc;
	*prealloc = NULL;
	}
	/*
	* 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);
	}
	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;
	stack->handle.valid = 1;
	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;
	}
	EXPORT_SYMBOL_GPL(depot_fetch_stack);

	/**
	* 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);
	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);
	alloc_flags \|= __GFP_NOWARN;
	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;
	}
	EXPORT_SYMBOL_GPL(depot_save_stack);