/* * 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;}