1 files changed, 284 insertions, 0 deletions
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
new file mode 100644
index 0000000..654c9d8
--- /dev/null
+++ b/lib/stackdepot.c
@@ -0,0 +1,284 @@
+/*
+ * 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;
+}