Merge tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:

 - Daniel Verkamp has contributed a memfd series ("mm/memfd: add
   F_SEAL_EXEC") which permits the setting of the memfd execute bit at
   memfd creation time, with the option of sealing the state of the X
   bit.

 - Peter Xu adds a patch series ("mm/hugetlb: Make huge_pte_offset()
   thread-safe for pmd unshare") which addresses a rare race condition
   related to PMD unsharing.

 - Several folioification patch serieses from Matthew Wilcox, Vishal
   Moola, Sidhartha Kumar and Lorenzo Stoakes

 - Johannes Weiner has a series ("mm: push down lock_page_memcg()")
   which does perform some memcg maintenance and cleanup work.

 - SeongJae Park has added DAMOS filtering to DAMON, with the series
   "mm/damon/core: implement damos filter".

   These filters provide users with finer-grained control over DAMOS's
   actions. SeongJae has also done some DAMON cleanup work.

 - Kairui Song adds a series ("Clean up and fixes for swap").

 - Vernon Yang contributed the series "Clean up and refinement for maple
   tree".

 - Yu Zhao has contributed the "mm: multi-gen LRU: memcg LRU" series. It
   adds to MGLRU an LRU of memcgs, to improve the scalability of global
   reclaim.

 - David Hildenbrand has added some userfaultfd cleanup work in the
   series "mm: uffd-wp + change_protection() cleanups".

 - Christoph Hellwig has removed the generic_writepages() library
   function in the series "remove generic_writepages".

 - Baolin Wang has performed some maintenance on the compaction code in
   his series "Some small improvements for compaction".

 - Sidhartha Kumar is doing some maintenance work on struct page in his
   series "Get rid of tail page fields".

 - David Hildenbrand contributed some cleanup, bugfixing and
   generalization of pte management and of pte debugging in his series
   "mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all architectures with
   swap PTEs".

 - Mel Gorman and Neil Brown have removed the __GFP_ATOMIC allocation
   flag in the series "Discard __GFP_ATOMIC".

 - Sergey Senozhatsky has improved zsmalloc's memory utilization with
   his series "zsmalloc: make zspage chain size configurable".

 - Joey Gouly has added prctl() support for prohibiting the creation of
   writeable+executable mappings.

   The previous BPF-based approach had shortcomings. See "mm: In-kernel
   support for memory-deny-write-execute (MDWE)".

 - Waiman Long did some kmemleak cleanup and bugfixing in the series
   "mm/kmemleak: Simplify kmemleak_cond_resched() & fix UAF".

 - T.J. Alumbaugh has contributed some MGLRU cleanup work in his series
   "mm: multi-gen LRU: improve".

 - Jiaqi Yan has provided some enhancements to our memory error
   statistics reporting, mainly by presenting the statistics on a
   per-node basis. See the series "Introduce per NUMA node memory error
   statistics".

 - Mel Gorman has a second and hopefully final shot at fixing a CPU-hog
   regression in compaction via his series "Fix excessive CPU usage
   during compaction".

 - Christoph Hellwig does some vmalloc maintenance work in the series
   "cleanup vfree and vunmap".

 - Christoph Hellwig has removed block_device_operations.rw_page() in
   ths series "remove ->rw_page".

 - We get some maple_tree improvements and cleanups in Liam Howlett's
   series "VMA tree type safety and remove __vma_adjust()".

 - Suren Baghdasaryan has done some work on the maintainability of our
   vm_flags handling in the series "introduce vm_flags modifier
   functions".

 - Some pagemap cleanup and generalization work in Mike Rapoport's
   series "mm, arch: add generic implementation of pfn_valid() for
   FLATMEM" and "fixups for generic implementation of pfn_valid()"

 - Baoquan He has done some work to make /proc/vmallocinfo and
   /proc/kcore better represent the real state of things in his series
   "mm/vmalloc.c: allow vread() to read out vm_map_ram areas".

 - Jason Gunthorpe rationalized the GUP system's interface to the rest
   of the kernel in the series "Simplify the external interface for
   GUP".

 - SeongJae Park wishes to migrate people from DAMON's debugfs interface
   over to its sysfs interface. To support this, we'll temporarily be
   printing warnings when people use the debugfs interface. See the
   series "mm/damon: deprecate DAMON debugfs interface".

 - Andrey Konovalov provided the accurately named "lib/stackdepot: fixes
   and clean-ups" series.

 - Huang Ying has provided a dramatic reduction in migration's TLB flush
   IPI rates with the series "migrate_pages(): batch TLB flushing".

 - Arnd Bergmann has some objtool fixups in "objtool warning fixes".

* tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (505 commits)
  include/linux/migrate.h: remove unneeded externs
  mm/memory_hotplug: cleanup return value handing in do_migrate_range()
  mm/uffd: fix comment in handling pte markers
  mm: change to return bool for isolate_movable_page()
  mm: hugetlb: change to return bool for isolate_hugetlb()
  mm: change to return bool for isolate_lru_page()
  mm: change to return bool for folio_isolate_lru()
  objtool: add UACCESS exceptions for __tsan_volatile_read/write
  kmsan: disable ftrace in kmsan core code
  kasan: mark addr_has_metadata __always_inline
  mm: memcontrol: rename memcg_kmem_enabled()
  sh: initialize max_mapnr
  m68k/nommu: add missing definition of ARCH_PFN_OFFSET
  mm: percpu: fix incorrect size in pcpu_obj_full_size()
  maple_tree: reduce stack usage with gcc-9 and earlier
  mm: page_alloc: call panic() when memoryless node allocation fails
  mm: multi-gen LRU: avoid futile retries
  migrate_pages: move THP/hugetlb migration support check to simplify code
  migrate_pages: batch flushing TLB
  migrate_pages: share more code between _unmap and _move
  ...

1 files changed, 324 insertions, 330 deletions

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 79e894cf8406..036da8e295d1 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -1,24 +1,19 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * Generic stack depot for storing stack traces.
+ * Stack depot - a stack trace storage that avoids duplication.
  *
- * 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 contiguous memory allocation.
+ * Internally, stack depot maintains a hash table of unique stacktraces. The
+ * stack traces themselves are stored contiguously one after another in a set
+ * of separate page allocations.
  *
  * Author: Alexander Potapenko <glider@google.com>
  * Copyright (C) 2016 Google, Inc.
  *
- * Based on code by Dmitry Chernenkov.
+ * Based on the code by Dmitry Chernenkov.
  */
 
+#define pr_fmt(fmt) "stackdepot: " fmt
+
 #include <linux/gfp.h>
 #include <linux/jhash.h>
 #include <linux/kernel.h>
@@ -34,243 +29,288 @@
 #include <linux/memblock.h>
 #include <linux/kasan-enabled.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 - STACK_DEPOT_EXTRA_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. */
+#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_POOLS_CAP 8192
+#define DEPOT_MAX_POOLS \
+	(((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
+	 (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)
+
+/* Compact structure that stores a reference to a stack. */
 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;
-		u32 extra : STACK_DEPOT_EXTRA_BITS;
+		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 hashtable */
-	u32 hash;			/* Hash in the hastable */
-	u32 size;			/* Number of frames in the stack */
+	struct stack_record *next;	/* Link in the hash table */
+	u32 hash;			/* Hash in the hash table */
+	u32 size;			/* Number of stored frames */
 	union handle_parts handle;
-	unsigned long entries[];	/* Variable-sized array of entries. */
+	unsigned long entries[];	/* Variable-sized array of frames */
 };
 
-static bool __stack_depot_want_early_init __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
+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;
 
-static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
-
-static int depot_index;
-static int next_slab_inited;
-static size_t depot_offset;
-static DEFINE_RAW_SPINLOCK(depot_lock);
-
-unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
-{
-	union handle_parts parts = { .handle = handle };
-
-	return parts.extra;
-}
-EXPORT_SYMBOL(stack_depot_get_extra_bits);
-
-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 stack_depot_save().
-		 */
-		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)
-{
-	struct stack_record *stack;
-	size_t required_size = struct_size(stack, entries, size);
-
-	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 stack_depot_save() 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;
-	stack->handle.extra = 0;
-	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
-	depot_offset += required_size;
-
-	return stack;
-}
-
-/* one hash table bucket entry per 16kB of memory */
-#define STACK_HASH_SCALE	14
-/* limited between 4k and 1M buckets */
-#define STACK_HASH_ORDER_MIN	12
-#define STACK_HASH_ORDER_MAX	20
+/* Use one hash table bucket per 16 KB of memory. */
+#define STACK_HASH_TABLE_SCALE 14
+/* Limit the number of buckets between 4K and 1M. */
+#define STACK_BUCKET_NUMBER_ORDER_MIN 12
+#define STACK_BUCKET_NUMBER_ORDER_MAX 20
+/* Initial seed for jhash2. */
 #define STACK_HASH_SEED 0x9747b28c
 
-static unsigned int stack_hash_order;
+/* Hash table of pointers to stored stack traces. */
+static struct stack_record **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;
 
-static bool stack_depot_disable;
-static struct stack_record **stack_table;
+/* Array of memory regions that store stack traces. */
+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);
+/*
+ * 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.
+ */
+static int next_pool_required = 1;
 
-static int __init is_stack_depot_disabled(char *str)
+static int __init disable_stack_depot(char *str)
 {
 	int ret;
 
-	ret = kstrtobool(str, &stack_depot_disable);
-	if (!ret && stack_depot_disable) {
-		pr_info("Stack Depot is disabled\n");
+	ret = kstrtobool(str, &stack_depot_disabled);
+	if (!ret && stack_depot_disabled) {
+		pr_info("disabled\n");
 		stack_table = NULL;
 	}
 	return 0;
 }
-early_param("stack_depot_disable", is_stack_depot_disabled);
+early_param("stack_depot_disable", disable_stack_depot);
 
-void __init stack_depot_want_early_init(void)
+void __init stack_depot_request_early_init(void)
 {
-	/* Too late to request early init now */
+	/* Too late to request early init now. */
 	WARN_ON(__stack_depot_early_init_passed);
 
-	__stack_depot_want_early_init = true;
+	__stack_depot_early_init_requested = true;
 }
 
+/* Allocates a hash table via memblock. Can only be used during early boot. */
 int __init stack_depot_early_init(void)
 {
 	unsigned long entries = 0;
 
-	/* This is supposed to be called only once, from mm_init() */
+	/* This function must be called only once, from mm_init(). */
 	if (WARN_ON(__stack_depot_early_init_passed))
 		return 0;
-
 	__stack_depot_early_init_passed = true;
 
-	if (kasan_enabled() && !stack_hash_order)
-		stack_hash_order = STACK_HASH_ORDER_MAX;
+	/*
+	 * 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.
+	 */
+	if (kasan_enabled() && !stack_bucket_number_order)
+		stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX;
 
-	if (!__stack_depot_want_early_init || stack_depot_disable)
+	if (!__stack_depot_early_init_requested || stack_depot_disabled)
 		return 0;
 
-	if (stack_hash_order)
-		entries = 1UL <<  stack_hash_order;
+	/*
+	 * If stack_bucket_number_order is not set, leave entries as 0 to rely
+	 * 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 *),
 						entries,
-						STACK_HASH_SCALE,
+						STACK_HASH_TABLE_SCALE,
 						HASH_EARLY | HASH_ZERO,
 						NULL,
 						&stack_hash_mask,
-						1UL << STACK_HASH_ORDER_MIN,
-						1UL << STACK_HASH_ORDER_MAX);
-
+						1UL << STACK_BUCKET_NUMBER_ORDER_MIN,
+						1UL << STACK_BUCKET_NUMBER_ORDER_MAX);
 	if (!stack_table) {
-		pr_err("Stack Depot hash table allocation failed, disabling\n");
-		stack_depot_disable = true;
+		pr_err("hash table allocation failed, disabling\n");
+		stack_depot_disabled = true;
 		return -ENOMEM;
 	}
 
 	return 0;
 }
 
+/* Allocates a hash table via kvcalloc. Can be used after boot. */
 int stack_depot_init(void)
 {
 	static DEFINE_MUTEX(stack_depot_init_mutex);
+	unsigned long entries;
 	int ret = 0;
 
 	mutex_lock(&stack_depot_init_mutex);
-	if (!stack_depot_disable && !stack_table) {
-		unsigned long entries;
-		int scale = STACK_HASH_SCALE;
-
-		if (stack_hash_order) {
-			entries = 1UL << stack_hash_order;
-		} else {
-			entries = nr_free_buffer_pages();
-			entries = roundup_pow_of_two(entries);
-
-			if (scale > PAGE_SHIFT)
-				entries >>= (scale - PAGE_SHIFT);
-			else
-				entries <<= (PAGE_SHIFT - scale);
-		}
 
-		if (entries < 1UL << STACK_HASH_ORDER_MIN)
-			entries = 1UL << STACK_HASH_ORDER_MIN;
-		if (entries > 1UL << STACK_HASH_ORDER_MAX)
-			entries = 1UL << STACK_HASH_ORDER_MAX;
-
-		pr_info("Stack Depot allocating hash table of %lu entries with kvcalloc\n",
-				entries);
-		stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL);
-		if (!stack_table) {
-			pr_err("Stack Depot hash table allocation failed, disabling\n");
-			stack_depot_disable = true;
-			ret = -ENOMEM;
-		}
-		stack_hash_mask = entries - 1;
+	if (stack_depot_disabled || stack_table)
+		goto out_unlock;
+
+	/*
+	 * Similarly to stack_depot_early_init, use stack_bucket_number_order
+	 * if assigned, and rely on automatic scaling otherwise.
+	 */
+	if (stack_bucket_number_order) {
+		entries = 1UL << stack_bucket_number_order;
+	} else {
+		int scale = STACK_HASH_TABLE_SCALE;
+
+		entries = nr_free_buffer_pages();
+		entries = roundup_pow_of_two(entries);
+
+		if (scale > PAGE_SHIFT)
+			entries >>= (scale - PAGE_SHIFT);
+		else
+			entries <<= (PAGE_SHIFT - scale);
+	}
+
+	if (entries < 1UL << STACK_BUCKET_NUMBER_ORDER_MIN)
+		entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MIN;
+	if (entries > 1UL << STACK_BUCKET_NUMBER_ORDER_MAX)
+		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);
+	if (!stack_table) {
+		pr_err("hash table allocation failed, disabling\n");
+		stack_depot_disabled = true;
+		ret = -ENOMEM;
+		goto out_unlock;
 	}
+	stack_hash_mask = entries - 1;
+
+out_unlock:
 	mutex_unlock(&stack_depot_init_mutex);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(stack_depot_init);
 
-/* Calculate hash for a stack */
+/* Uses preallocated memory to initialize a new stack depot pool. */
+static void depot_init_pool(void **prealloc)
+{
+	/*
+	 * If the next pool is already initialized 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))
+		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;
+		*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);
+	}
+}
+
+/* Allocates a new stack in a stack depot pool. */
+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);
+
+	/* 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;
+		}
+
+		/*
+		 * 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);
+	}
+
+	/* Assign the preallocated memory to a pool if required. */
+	if (*prealloc)
+		depot_init_pool(prealloc);
+
+	/* Check if we have a pool to save the stack trace. */
+	if (stack_pools[pool_index] == NULL)
+		return NULL;
+
+	/* 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;
+	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
+	pool_offset += required_size;
+
+	return stack;
+}
+
+/* Calculates the hash for a stack. */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
 {
 	return jhash2((u32 *)entries,
@@ -278,9 +318,9 @@ static inline u32 hash_stack(unsigned long *entries, unsigned int size)
 		      STACK_HASH_SEED);
 }
 
-/* Use our own, non-instrumented version of memcmp().
- *
- * We actually don't care about the order, just the equality.
+/*
+ * Non-instrumented version of memcmp().
+ * Does not check the lexicographical order, only the equality.
  */
 static inline
 int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
@@ -293,7 +333,7 @@ int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
 	return 0;
 }
 
-/* Find a stack that is equal to the one stored in entries in the hash */
+/* Finds a stack in a bucket of the hash table. */
 static inline struct stack_record *find_stack(struct stack_record *bucket,
 					     unsigned long *entries, int size,
 					     u32 hash)
@@ -309,116 +349,8 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
 	return NULL;
 }
 
-/**
- * stack_depot_snprint - print stack entries from a depot into a buffer
- *
- * @handle:	Stack depot handle which was returned from
- *		stack_depot_save().
- * @buf:	Pointer to the print buffer
- *
- * @size:	Size of the print buffer
- *
- * @spaces:	Number of leading spaces to print
- *
- * Return:	Number of bytes printed.
- */
-int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
-		       int spaces)
-{
-	unsigned long *entries;
-	unsigned int nr_entries;
-
-	nr_entries = stack_depot_fetch(handle, &entries);
-	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
-						spaces) : 0;
-}
-EXPORT_SYMBOL_GPL(stack_depot_snprint);
-
-/**
- * stack_depot_print - print stack entries from a depot
- *
- * @stack:		Stack depot handle which was returned from
- *			stack_depot_save().
- *
- */
-void stack_depot_print(depot_stack_handle_t stack)
-{
-	unsigned long *entries;
-	unsigned int nr_entries;
-
-	nr_entries = stack_depot_fetch(stack, &entries);
-	if (nr_entries > 0)
-		stack_trace_print(entries, nr_entries, 0);
-}
-EXPORT_SYMBOL_GPL(stack_depot_print);
-
-/**
- * stack_depot_fetch - Fetch stack entries from a depot
- *
- * @handle:		Stack depot handle which was returned from
- *			stack_depot_save().
- * @entries:		Pointer to store the entries address
- *
- * Return: The number of trace entries for this depot.
- */
-unsigned int stack_depot_fetch(depot_stack_handle_t handle,
-			       unsigned long **entries)
-{
-	union handle_parts parts = { .handle = handle };
-	void *slab;
-	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
-	struct stack_record *stack;
-
-	*entries = NULL;
-	if (!handle)
-		return 0;
-
-	if (parts.slabindex > depot_index) {
-		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
-			parts.slabindex, depot_index, handle);
-		return 0;
-	}
-	slab = stack_slabs[parts.slabindex];
-	if (!slab)
-		return 0;
-	stack = slab + offset;
-
-	*entries = stack->entries;
-	return stack->size;
-}
-EXPORT_SYMBOL_GPL(stack_depot_fetch);
-
-/**
- * __stack_depot_save - Save a stack trace from an array
- *
- * @entries:		Pointer to storage array
- * @nr_entries:		Size of the storage array
- * @extra_bits:		Flags to store in unused bits of depot_stack_handle_t
- * @alloc_flags:	Allocation gfp flags
- * @can_alloc:		Allocate stack slabs (increased chance of failure if false)
- *
- * Saves a stack trace from @entries array of size @nr_entries. If @can_alloc is
- * %true, is allowed to replenish the stack slab pool in case no space is left
- * (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids
- * any allocations and will fail if no space is left to store the stack trace.
- *
- * If the stack trace in @entries is from an interrupt, only the portion up to
- * interrupt entry is saved.
- *
- * Additional opaque flags can be passed in @extra_bits, stored in the unused
- * bits of the stack handle, and retrieved using stack_depot_get_extra_bits()
- * without calling stack_depot_fetch().
- *
- * Context: Any context, but setting @can_alloc to %false is required if
- *          alloc_pages() cannot be used from the current context. Currently
- *          this is the case from contexts where neither %GFP_ATOMIC nor
- *          %GFP_NOWAIT can be used (NMI, raw_spin_lock).
- *
- * Return: The handle of the stack struct stored in depot, 0 on failure.
- */
 depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 					unsigned int nr_entries,
-					unsigned int extra_bits,
 					gfp_t alloc_flags, bool can_alloc)
 {
 	struct stack_record *found = NULL, **bucket;
@@ -430,15 +362,15 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 
 	/*
 	 * If this stack trace is from an interrupt, including anything before
-	 * interrupt entry usually leads to unbounded stackdepot growth.
+	 * interrupt entry usually leads to unbounded stack depot growth.
 	 *
-	 * Because use of filter_irq_stacks() is a requirement to ensure
-	 * stackdepot can efficiently deduplicate interrupt stacks, always
-	 * filter_irq_stacks() to simplify all callers' use of stackdepot.
+	 * Since use of filter_irq_stacks() is a requirement to ensure stack
+	 * depot can efficiently deduplicate interrupt stacks, always
+	 * filter_irq_stacks() to simplify all callers' use of stack depot.
 	 */
 	nr_entries = filter_irq_stacks(entries, nr_entries);
 
-	if (unlikely(nr_entries == 0) || stack_depot_disable)
+	if (unlikely(nr_entries == 0) || stack_depot_disabled)
 		goto fast_exit;
 
 	hash = hash_stack(entries, nr_entries);
@@ -449,20 +381,18 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 	 * The smp_load_acquire() here pairs with smp_store_release() to
 	 * |bucket| below.
 	 */
-	found = find_stack(smp_load_acquire(bucket), entries,
-			   nr_entries, hash);
+	found = find_stack(smp_load_acquire(bucket), entries, 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.
+	 * 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_slab_inited| in depot_alloc_stack() and init_stack_slab().
+	 * |next_pool_inited| in depot_alloc_stack() and depot_init_pool().
 	 */
-	if (unlikely(can_alloc && !smp_load_acquire(&next_slab_inited))) {
+	if (unlikely(can_alloc && smp_load_acquire(&next_pool_required))) {
 		/*
 		 * Zero out zone modifiers, as we don't have specific zone
 		 * requirements. Keep the flags related to allocation in atomic
@@ -471,16 +401,17 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 		alloc_flags &= ~GFP_ZONEMASK;
 		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
 		alloc_flags |= __GFP_NOWARN;
-		page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
+		page = alloc_pages(alloc_flags, DEPOT_POOL_ORDER);
 		if (page)
 			prealloc = page_address(page);
 	}
 
-	raw_spin_lock_irqsave(&depot_lock, flags);
+	raw_spin_lock_irqsave(&pool_lock, flags);
 
 	found = find_stack(*bucket, entries, nr_entries, hash);
 	if (!found) {
-		struct stack_record *new = depot_alloc_stack(entries, nr_entries, hash, &prealloc);
+		struct stack_record *new =
+			depot_alloc_stack(entries, nr_entries, hash, &prealloc);
 
 		if (new) {
 			new->next = *bucket;
@@ -493,43 +424,106 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 		}
 	} else if (prealloc) {
 		/*
-		 * We didn't need to store this stack trace, but let's keep
-		 * the preallocated memory for the future.
+		 * Stack depot already contains this stack trace, but let's
+		 * keep the preallocated memory for the future.
 		 */
-		WARN_ON(!init_stack_slab(&prealloc));
+		depot_init_pool(&prealloc);
 	}
 
-	raw_spin_unlock_irqrestore(&depot_lock, flags);
+	raw_spin_unlock_irqrestore(&pool_lock, flags);
 exit:
 	if (prealloc) {
-		/* Nobody used this memory, ok to free it. */
-		free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
+		/* 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:
-	retval.extra = extra_bits;
-
 	return retval.handle;
 }
 EXPORT_SYMBOL_GPL(__stack_depot_save);
 
-/**
- * stack_depot_save - Save a stack trace from an array
- *
- * @entries:		Pointer to storage array
- * @nr_entries:		Size of the storage array
- * @alloc_flags:	Allocation gfp flags
- *
- * Context: Contexts where allocations via alloc_pages() are allowed.
- *          See __stack_depot_save() for more details.
- *
- * Return: The handle of the stack struct stored in depot, 0 on failure.
- */
 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, 0, alloc_flags, true);
+	return __stack_depot_save(entries, nr_entries, alloc_flags, true);
 }
 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;
+
+	*entries = NULL;
+	if (!handle)
+		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;
+
+	*entries = stack->entries;
+	return stack->size;
+}
+EXPORT_SYMBOL_GPL(stack_depot_fetch);
+
+void stack_depot_print(depot_stack_handle_t stack)
+{
+	unsigned long *entries;
+	unsigned int nr_entries;
+
+	nr_entries = stack_depot_fetch(stack, &entries);
+	if (nr_entries > 0)
+		stack_trace_print(entries, nr_entries, 0);
+}
+EXPORT_SYMBOL_GPL(stack_depot_print);
+
+int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
+		       int spaces)
+{
+	unsigned long *entries;
+	unsigned int nr_entries;
+
+	nr_entries = stack_depot_fetch(handle, &entries);
+	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
+						spaces) : 0;
+}
+EXPORT_SYMBOL_GPL(stack_depot_snprint);
+
+depot_stack_handle_t __must_check stack_depot_set_extra_bits(
+			depot_stack_handle_t handle, unsigned int extra_bits)
+{
+	union handle_parts parts = { .handle = handle };
+
+	/* Don't set extra bits on empty handles. */
+	if (!handle)
+		return 0;
+
+	parts.extra = extra_bits;
+	return parts.handle;
+}
+EXPORT_SYMBOL(stack_depot_set_extra_bits);
+
+unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
+{
+	union handle_parts parts = { .handle = handle };
+
+	return parts.extra;
+}
+EXPORT_SYMBOL(stack_depot_get_extra_bits);