1 files changed, 306 insertions, 155 deletions

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 2f5aa851834e..a0be5d05c7f0 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -18,11 +18,14 @@
 #include <linux/jhash.h>
 #include <linux/kernel.h>
 #include <linux/kmsan.h>
+#include <linux/list.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/percpu.h>
 #include <linux/printk.h>
+#include <linux/refcount.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/stacktrace.h>
 #include <linux/stackdepot.h>
 #include <linux/string.h>
@@ -32,14 +35,23 @@
 
 #define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
 
-#define DEPOT_VALID_BITS 1
 #define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
 #define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
 #define DEPOT_STACK_ALIGN 4
 #define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
-#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_VALID_BITS - \
-			       DEPOT_OFFSET_BITS - STACK_DEPOT_EXTRA_BITS)
+#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
+			       STACK_DEPOT_EXTRA_BITS)
+#if IS_ENABLED(CONFIG_KMSAN) && CONFIG_STACKDEPOT_MAX_FRAMES >= 32
+/*
+ * KMSAN is frequently used in fuzzing scenarios and thus saves a lot of stack
+ * traces. As KMSAN does not support evicting stack traces from the stack
+ * depot, the stack depot capacity might be reached quickly with large stack
+ * records. Adjust the maximum number of stack depot pools for this case.
+ */
+#define DEPOT_POOLS_CAP (8192 * (CONFIG_STACKDEPOT_MAX_FRAMES / 16))
+#else
 #define DEPOT_POOLS_CAP 8192
+#endif
 #define DEPOT_MAX_POOLS \
 	(((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
 	 (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)
@@ -50,19 +62,22 @@ union handle_parts {
 	struct {
 		u32 pool_index	: DEPOT_POOL_INDEX_BITS;
 		u32 offset	: DEPOT_OFFSET_BITS;
-		u32 valid	: DEPOT_VALID_BITS;
 		u32 extra	: STACK_DEPOT_EXTRA_BITS;
 	};
 };
 
 struct stack_record {
-	struct stack_record *next;	/* Link in the hash table */
-	u32 hash;			/* Hash in the hash table */
+	struct list_head list;		/* Links in hash table or freelist */
+	u32 hash;			/* Hash in hash table */
 	u32 size;			/* Number of stored frames */
 	union handle_parts handle;
-	unsigned long entries[];	/* Variable-sized array of frames */
+	refcount_t count;
+	unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES];	/* Frames */
 };
 
+#define DEPOT_STACK_RECORD_SIZE \
+	ALIGN(sizeof(struct stack_record), 1 << DEPOT_STACK_ALIGN)
+
 static bool stack_depot_disabled;
 static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
 static bool __stack_depot_early_init_passed __initdata;
@@ -75,40 +90,34 @@ static bool __stack_depot_early_init_passed __initdata;
 /* Initial seed for jhash2. */
 #define STACK_HASH_SEED 0x9747b28c
 
-/* Hash table of pointers to stored stack traces. */
-static struct stack_record **stack_table;
+/* Hash table of stored stack records. */
+static struct list_head *stack_table;
 /* Fixed order of the number of table buckets. Used when KASAN is enabled. */
 static unsigned int stack_bucket_number_order;
 /* Hash mask for indexing the table. */
 static unsigned int stack_hash_mask;
 
-/* Array of memory regions that store stack traces. */
+/* Array of memory regions that store stack records. */
 static void *stack_pools[DEPOT_MAX_POOLS];
-/* Currently used pool in stack_pools. */
-static int pool_index;
-/* Offset to the unused space in the currently used pool. */
-static size_t pool_offset;
-/* Lock that protects the variables above. */
-static DEFINE_RAW_SPINLOCK(pool_lock);
+/* Newly allocated pool that is not yet added to stack_pools. */
+static void *new_pool;
+/* Number of pools in stack_pools. */
+static int pools_num;
+/* Freelist of stack records within stack_pools. */
+static LIST_HEAD(free_stacks);
 /*
  * Stack depot tries to keep an extra pool allocated even before it runs out
- * of space in the currently used pool.
- * This flag marks that this next extra pool needs to be allocated and
- * initialized. It has the value 0 when either the next pool is not yet
- * initialized or the limit on the number of pools is reached.
+ * of space in the currently used pool. This flag marks whether this extra pool
+ * needs to be allocated. It has the value 0 when either an extra pool is not
+ * yet allocated or if the limit on the number of pools is reached.
  */
-static int next_pool_required = 1;
+static bool new_pool_required = true;
+/* Lock that protects the variables above. */
+static DEFINE_RWLOCK(pool_rwlock);
 
 static int __init disable_stack_depot(char *str)
 {
-	int ret;
-
-	ret = kstrtobool(str, &stack_depot_disabled);
-	if (!ret && stack_depot_disabled) {
-		pr_info("disabled\n");
-		stack_table = NULL;
-	}
-	return 0;
+	return kstrtobool(str, &stack_depot_disabled);
 }
 early_param("stack_depot_disable", disable_stack_depot);
 
@@ -120,6 +129,15 @@ void __init stack_depot_request_early_init(void)
 	__stack_depot_early_init_requested = true;
 }
 
+/* Initialize list_head's within the hash table. */
+static void init_stack_table(unsigned long entries)
+{
+	unsigned long i;
+
+	for (i = 0; i < entries; i++)
+		INIT_LIST_HEAD(&stack_table[i]);
+}
+
 /* Allocates a hash table via memblock. Can only be used during early boot. */
 int __init stack_depot_early_init(void)
 {
@@ -131,6 +149,15 @@ int __init stack_depot_early_init(void)
 	__stack_depot_early_init_passed = true;
 
 	/*
+	 * Print disabled message even if early init has not been requested:
+	 * stack_depot_init() will not print one.
+	 */
+	if (stack_depot_disabled) {
+		pr_info("disabled\n");
+		return 0;
+	}
+
+	/*
 	 * If KASAN is enabled, use the maximum order: KASAN is frequently used
 	 * in fuzzing scenarios, which leads to a large number of different
 	 * stack traces being stored in stack depot.
@@ -138,21 +165,25 @@ int __init stack_depot_early_init(void)
 	if (kasan_enabled() && !stack_bucket_number_order)
 		stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX;
 
-	if (!__stack_depot_early_init_requested || stack_depot_disabled)
+	/*
+	 * Check if early init has been requested after setting
+	 * stack_bucket_number_order: stack_depot_init() uses its value.
+	 */
+	if (!__stack_depot_early_init_requested)
 		return 0;
 
 	/*
 	 * If stack_bucket_number_order is not set, leave entries as 0 to rely
-	 * on the automatic calculations performed by alloc_large_system_hash.
+	 * on the automatic calculations performed by alloc_large_system_hash().
 	 */
 	if (stack_bucket_number_order)
 		entries = 1UL << stack_bucket_number_order;
 	pr_info("allocating hash table via alloc_large_system_hash\n");
 	stack_table = alloc_large_system_hash("stackdepot",
-						sizeof(struct stack_record *),
+						sizeof(struct list_head),
 						entries,
 						STACK_HASH_TABLE_SCALE,
-						HASH_EARLY | HASH_ZERO,
+						HASH_EARLY,
 						NULL,
 						&stack_hash_mask,
 						1UL << STACK_BUCKET_NUMBER_ORDER_MIN,
@@ -162,6 +193,14 @@ int __init stack_depot_early_init(void)
 		stack_depot_disabled = true;
 		return -ENOMEM;
 	}
+	if (!entries) {
+		/*
+		 * Obtain the number of entries that was calculated by
+		 * alloc_large_system_hash().
+		 */
+		entries = stack_hash_mask + 1;
+	}
+	init_stack_table(entries);
 
 	return 0;
 }
@@ -202,7 +241,7 @@ int stack_depot_init(void)
 		entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MAX;
 
 	pr_info("allocating hash table of %lu entries via kvcalloc\n", entries);
-	stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL);
+	stack_table = kvcalloc(entries, sizeof(struct list_head), GFP_KERNEL);
 	if (!stack_table) {
 		pr_err("hash table allocation failed, disabling\n");
 		stack_depot_disabled = true;
@@ -210,6 +249,7 @@ int stack_depot_init(void)
 		goto out_unlock;
 	}
 	stack_hash_mask = entries - 1;
+	init_stack_table(entries);
 
 out_unlock:
 	mutex_unlock(&stack_depot_init_mutex);
@@ -218,41 +258,103 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(stack_depot_init);
 
-/* Uses preallocated memory to initialize a new stack depot pool. */
-static void depot_init_pool(void **prealloc)
+/* Initializes a stack depol pool. */
+static void depot_init_pool(void *pool)
 {
+	int offset;
+
+	lockdep_assert_held_write(&pool_rwlock);
+
+	WARN_ON(!list_empty(&free_stacks));
+
+	/* Initialize handles and link stack records into the freelist. */
+	for (offset = 0; offset <= DEPOT_POOL_SIZE - DEPOT_STACK_RECORD_SIZE;
+	     offset += DEPOT_STACK_RECORD_SIZE) {
+		struct stack_record *stack = pool + offset;
+
+		stack->handle.pool_index = pools_num;
+		stack->handle.offset = offset >> DEPOT_STACK_ALIGN;
+		stack->handle.extra = 0;
+
+		list_add(&stack->list, &free_stacks);
+	}
+
+	/* Save reference to the pool to be used by depot_fetch_stack(). */
+	stack_pools[pools_num] = pool;
+	pools_num++;
+}
+
+/* Keeps the preallocated memory to be used for a new stack depot pool. */
+static void depot_keep_new_pool(void **prealloc)
+{
+	lockdep_assert_held_write(&pool_rwlock);
+
 	/*
-	 * If the next pool is already initialized or the maximum number of
+	 * If a new pool is already saved or the maximum number of
 	 * pools is reached, do not use the preallocated memory.
-	 * smp_load_acquire() here pairs with smp_store_release() below and
-	 * in depot_alloc_stack().
 	 */
-	if (!smp_load_acquire(&next_pool_required))
+	if (!new_pool_required)
 		return;
 
-	/* Check if the current pool is not yet allocated. */
-	if (stack_pools[pool_index] == NULL) {
-		/* Use the preallocated memory for the current pool. */
-		stack_pools[pool_index] = *prealloc;
+	/*
+	 * Use the preallocated memory for the new pool
+	 * as long as we do not exceed the maximum number of pools.
+	 */
+	if (pools_num < DEPOT_MAX_POOLS) {
+		new_pool = *prealloc;
 		*prealloc = NULL;
-	} else {
-		/*
-		 * Otherwise, use the preallocated memory for the next pool
-		 * as long as we do not exceed the maximum number of pools.
-		 */
-		if (pool_index + 1 < DEPOT_MAX_POOLS) {
-			stack_pools[pool_index + 1] = *prealloc;
-			*prealloc = NULL;
-		}
-		/*
-		 * At this point, either the next pool is initialized or the
-		 * maximum number of pools is reached. In either case, take
-		 * note that initializing another pool is not required.
-		 * This smp_store_release pairs with smp_load_acquire() above
-		 * and in stack_depot_save().
-		 */
-		smp_store_release(&next_pool_required, 0);
 	}
+
+	/*
+	 * At this point, either a new pool is kept or the maximum
+	 * number of pools is reached. In either case, take note that
+	 * keeping another pool is not required.
+	 */
+	new_pool_required = false;
+}
+
+/* Updates references to the current and the next stack depot pools. */
+static bool depot_update_pools(void **prealloc)
+{
+	lockdep_assert_held_write(&pool_rwlock);
+
+	/* Check if we still have objects in the freelist. */
+	if (!list_empty(&free_stacks))
+		goto out_keep_prealloc;
+
+	/* Check if we have a new pool saved and use it. */
+	if (new_pool) {
+		depot_init_pool(new_pool);
+		new_pool = NULL;
+
+		/* Take note that we might need a new new_pool. */
+		if (pools_num < DEPOT_MAX_POOLS)
+			new_pool_required = true;
+
+		/* Try keeping the preallocated memory for new_pool. */
+		goto out_keep_prealloc;
+	}
+
+	/* Bail out if we reached the pool limit. */
+	if (unlikely(pools_num >= DEPOT_MAX_POOLS)) {
+		WARN_ONCE(1, "Stack depot reached limit capacity");
+		return false;
+	}
+
+	/* Check if we have preallocated memory and use it. */
+	if (*prealloc) {
+		depot_init_pool(*prealloc);
+		*prealloc = NULL;
+		return true;
+	}
+
+	return false;
+
+out_keep_prealloc:
+	/* Keep the preallocated memory for a new pool if required. */
+	if (*prealloc)
+		depot_keep_new_pool(prealloc);
+	return true;
 }
 
 /* Allocates a new stack in a stack depot pool. */
@@ -260,62 +362,72 @@ static struct stack_record *
 depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
 {
 	struct stack_record *stack;
-	size_t required_size = struct_size(stack, entries, size);
 
-	required_size = ALIGN(required_size, 1 << DEPOT_STACK_ALIGN);
+	lockdep_assert_held_write(&pool_rwlock);
 
-	/* Check if there is not enough space in the current pool. */
-	if (unlikely(pool_offset + required_size > DEPOT_POOL_SIZE)) {
-		/* Bail out if we reached the pool limit. */
-		if (unlikely(pool_index + 1 >= DEPOT_MAX_POOLS)) {
-			WARN_ONCE(1, "Stack depot reached limit capacity");
-			return NULL;
-		}
+	/* Update current and new pools if required and possible. */
+	if (!depot_update_pools(prealloc))
+		return NULL;
 
-		/*
-		 * Move on to the next pool.
-		 * WRITE_ONCE pairs with potential concurrent read in
-		 * stack_depot_fetch().
-		 */
-		WRITE_ONCE(pool_index, pool_index + 1);
-		pool_offset = 0;
-		/*
-		 * If the maximum number of pools is not reached, take note
-		 * that the next pool needs to initialized.
-		 * smp_store_release() here pairs with smp_load_acquire() in
-		 * stack_depot_save() and depot_init_pool().
-		 */
-		if (pool_index + 1 < DEPOT_MAX_POOLS)
-			smp_store_release(&next_pool_required, 1);
-	}
+	/* Check if we have a stack record to save the stack trace. */
+	if (list_empty(&free_stacks))
+		return NULL;
 
-	/* Assign the preallocated memory to a pool if required. */
-	if (*prealloc)
-		depot_init_pool(prealloc);
+	/* Get and unlink the first entry from the freelist. */
+	stack = list_first_entry(&free_stacks, struct stack_record, list);
+	list_del(&stack->list);
 
-	/* Check if we have a pool to save the stack trace. */
-	if (stack_pools[pool_index] == NULL)
-		return NULL;
+	/* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */
+	if (size > CONFIG_STACKDEPOT_MAX_FRAMES)
+		size = CONFIG_STACKDEPOT_MAX_FRAMES;
 
 	/* Save the stack trace. */
-	stack = stack_pools[pool_index] + pool_offset;
 	stack->hash = hash;
 	stack->size = size;
-	stack->handle.pool_index = pool_index;
-	stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
-	stack->handle.valid = 1;
-	stack->handle.extra = 0;
+	/* stack->handle is already filled in by depot_init_pool(). */
+	refcount_set(&stack->count, 1);
 	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
-	pool_offset += required_size;
+
 	/*
 	 * Let KMSAN know the stored stack record is initialized. This shall
 	 * prevent false positive reports if instrumented code accesses it.
 	 */
-	kmsan_unpoison_memory(stack, required_size);
+	kmsan_unpoison_memory(stack, DEPOT_STACK_RECORD_SIZE);
 
 	return stack;
 }
 
+static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
+{
+	union handle_parts parts = { .handle = handle };
+	void *pool;
+	size_t offset = parts.offset << DEPOT_STACK_ALIGN;
+	struct stack_record *stack;
+
+	lockdep_assert_held(&pool_rwlock);
+
+	if (parts.pool_index > pools_num) {
+		WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
+		     parts.pool_index, pools_num, handle);
+		return NULL;
+	}
+
+	pool = stack_pools[parts.pool_index];
+	if (!pool)
+		return NULL;
+
+	stack = pool + offset;
+	return stack;
+}
+
+/* Links stack into the freelist. */
+static void depot_free_stack(struct stack_record *stack)
+{
+	lockdep_assert_held_write(&pool_rwlock);
+
+	list_add(&stack->list, &free_stacks);
+}
+
 /* Calculates the hash for a stack. */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
 {
@@ -340,13 +452,17 @@ int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
 }
 
 /* Finds a stack in a bucket of the hash table. */
-static inline struct stack_record *find_stack(struct stack_record *bucket,
+static inline struct stack_record *find_stack(struct list_head *bucket,
 					     unsigned long *entries, int size,
 					     u32 hash)
 {
+	struct list_head *pos;
 	struct stack_record *found;
 
-	for (found = bucket; found; found = found->next) {
+	lockdep_assert_held(&pool_rwlock);
+
+	list_for_each(pos, bucket) {
+		found = list_entry(pos, struct stack_record, list);
 		if (found->hash == hash &&
 		    found->size == size &&
 		    !stackdepot_memcmp(entries, found->entries, size))
@@ -355,17 +471,24 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
 	return NULL;
 }
 
-depot_stack_handle_t __stack_depot_save(unsigned long *entries,
-					unsigned int nr_entries,
-					gfp_t alloc_flags, bool can_alloc)
+depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
+					    unsigned int nr_entries,
+					    gfp_t alloc_flags,
+					    depot_flags_t depot_flags)
 {
-	struct stack_record *found = NULL, **bucket;
-	union handle_parts retval = { .handle = 0 };
+	struct list_head *bucket;
+	struct stack_record *found = NULL;
+	depot_stack_handle_t handle = 0;
 	struct page *page = NULL;
 	void *prealloc = NULL;
+	bool can_alloc = depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC;
+	bool need_alloc = false;
 	unsigned long flags;
 	u32 hash;
 
+	if (WARN_ON(depot_flags & ~STACK_DEPOT_FLAGS_MASK))
+		return 0;
+
 	/*
 	 * If this stack trace is from an interrupt, including anything before
 	 * interrupt entry usually leads to unbounded stack depot growth.
@@ -377,28 +500,36 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 	nr_entries = filter_irq_stacks(entries, nr_entries);
 
 	if (unlikely(nr_entries == 0) || stack_depot_disabled)
-		goto fast_exit;
+		return 0;
 
 	hash = hash_stack(entries, 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), entries, nr_entries, hash);
-	if (found)
+	read_lock_irqsave(&pool_rwlock, flags);
+	printk_deferred_enter();
+
+	/* Fast path: look the stack trace up without full locking. */
+	found = find_stack(bucket, entries, nr_entries, hash);
+	if (found) {
+		if (depot_flags & STACK_DEPOT_FLAG_GET)
+			refcount_inc(&found->count);
+		printk_deferred_exit();
+		read_unlock_irqrestore(&pool_rwlock, flags);
 		goto exit;
+	}
+
+	/* Take note if another stack pool needs to be allocated. */
+	if (new_pool_required)
+		need_alloc = true;
+
+	printk_deferred_exit();
+	read_unlock_irqrestore(&pool_rwlock, flags);
 
 	/*
-	 * Check if another stack pool needs to be initialized. If so, allocate
-	 * the memory now - we won't be able to do that under the lock.
-	 *
-	 * The smp_load_acquire() here pairs with smp_store_release() to
-	 * |next_pool_inited| in depot_alloc_stack() and depot_init_pool().
+	 * Allocate memory for a new pool if required now:
+	 * we won't be able to do that under the lock.
 	 */
-	if (unlikely(can_alloc && smp_load_acquire(&next_pool_required))) {
+	if (unlikely(can_alloc && need_alloc)) {
 		/*
 		 * Zero out zone modifiers, as we don't have specific zone
 		 * requirements. Keep the flags related to allocation in atomic
@@ -412,63 +543,56 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 			prealloc = page_address(page);
 	}
 
-	raw_spin_lock_irqsave(&pool_lock, flags);
+	write_lock_irqsave(&pool_rwlock, flags);
+	printk_deferred_enter();
 
-	found = find_stack(*bucket, entries, nr_entries, hash);
+	found = find_stack(bucket, entries, nr_entries, hash);
 	if (!found) {
 		struct stack_record *new =
 			depot_alloc_stack(entries, nr_entries, hash, &prealloc);
 
 		if (new) {
-			new->next = *bucket;
-			/*
-			 * This smp_store_release() pairs with
-			 * smp_load_acquire() from |bucket| above.
-			 */
-			smp_store_release(bucket, new);
+			list_add(&new->list, bucket);
 			found = new;
 		}
-	} else if (prealloc) {
+	} else {
+		if (depot_flags & STACK_DEPOT_FLAG_GET)
+			refcount_inc(&found->count);
 		/*
 		 * Stack depot already contains this stack trace, but let's
-		 * keep the preallocated memory for the future.
+		 * keep the preallocated memory for future.
 		 */
-		depot_init_pool(&prealloc);
+		if (prealloc)
+			depot_keep_new_pool(&prealloc);
 	}
 
-	raw_spin_unlock_irqrestore(&pool_lock, flags);
+	printk_deferred_exit();
+	write_unlock_irqrestore(&pool_rwlock, flags);
 exit:
 	if (prealloc) {
 		/* Stack depot didn't use this memory, free it. */
 		free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
 	}
 	if (found)
-		retval.handle = found->handle.handle;
-fast_exit:
-	return retval.handle;
+		handle = found->handle.handle;
+	return handle;
 }
-EXPORT_SYMBOL_GPL(__stack_depot_save);
+EXPORT_SYMBOL_GPL(stack_depot_save_flags);
 
 depot_stack_handle_t stack_depot_save(unsigned long *entries,
 				      unsigned int nr_entries,
 				      gfp_t alloc_flags)
 {
-	return __stack_depot_save(entries, nr_entries, alloc_flags, true);
+	return stack_depot_save_flags(entries, nr_entries, alloc_flags,
+				      STACK_DEPOT_FLAG_CAN_ALLOC);
 }
 EXPORT_SYMBOL_GPL(stack_depot_save);
 
 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 			       unsigned long **entries)
 {
-	union handle_parts parts = { .handle = handle };
-	/*
-	 * READ_ONCE pairs with potential concurrent write in
-	 * depot_alloc_stack.
-	 */
-	int pool_index_cached = READ_ONCE(pool_index);
-	void *pool;
-	size_t offset = parts.offset << DEPOT_STACK_ALIGN;
 	struct stack_record *stack;
+	unsigned long flags;
 
 	*entries = NULL;
 	/*
@@ -477,24 +601,51 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 	 */
 	kmsan_unpoison_memory(entries, sizeof(*entries));
 
-	if (!handle)
+	if (!handle || stack_depot_disabled)
 		return 0;
 
-	if (parts.pool_index > pool_index_cached) {
-		WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
-			parts.pool_index, pool_index_cached, handle);
-		return 0;
-	}
-	pool = stack_pools[parts.pool_index];
-	if (!pool)
-		return 0;
-	stack = pool + offset;
+	read_lock_irqsave(&pool_rwlock, flags);
+	printk_deferred_enter();
+
+	stack = depot_fetch_stack(handle);
+
+	printk_deferred_exit();
+	read_unlock_irqrestore(&pool_rwlock, flags);
 
 	*entries = stack->entries;
 	return stack->size;
 }
 EXPORT_SYMBOL_GPL(stack_depot_fetch);
 
+void stack_depot_put(depot_stack_handle_t handle)
+{
+	struct stack_record *stack;
+	unsigned long flags;
+
+	if (!handle || stack_depot_disabled)
+		return;
+
+	write_lock_irqsave(&pool_rwlock, flags);
+	printk_deferred_enter();
+
+	stack = depot_fetch_stack(handle);
+	if (WARN_ON(!stack))
+		goto out;
+
+	if (refcount_dec_and_test(&stack->count)) {
+		/* Unlink stack from the hash table. */
+		list_del(&stack->list);
+
+		/* Free stack. */
+		depot_free_stack(stack);
+	}
+
+out:
+	printk_deferred_exit();
+	write_unlock_irqrestore(&pool_rwlock, flags);
+}
+EXPORT_SYMBOL_GPL(stack_depot_put);
+
 void stack_depot_print(depot_stack_handle_t stack)
 {
 	unsigned long *entries;