+ lib-stackdepot-rework-helpers-for-depot_alloc_stack.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: lib/stackdepot: rework helpers for depot_alloc_stack
has been added to the -mm mm-unstable branch.  Its filename is
     lib-stackdepot-rework-helpers-for-depot_alloc_stack.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-stackdepot-rework-helpers-for-depot_alloc_stack.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Andrey Konovalov <andreyknvl@google.com>
Subject: lib/stackdepot: rework helpers for depot_alloc_stack
Date: Wed, 13 Sep 2023 19:14:32 +0200

Split code in depot_alloc_stack and depot_init_pool into 3 functions:

1. depot_keep_next_pool that keeps preallocated memory for the next pool
   if required.

2. depot_update_pools that moves on to the next pool if there's no space
   left in the current pool, uses preallocated memory for the new current
   pool if required, and calls depot_keep_next_pool otherwise.

3. depot_alloc_stack that calls depot_update_pools and then allocates
   a stack record as before.

This makes it somewhat easier to follow the logic of depot_alloc_stack
and also serves as a preparation for implementing the eviction of stack
records from the stack depot.

Link: https://lkml.kernel.org/r/bbf482643e882f9f870d80cb35342c61955ea291.1694625260.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/stackdepot.c |   87 +++++++++++++++++++++++++--------------------
 1 file changed, 49 insertions(+), 38 deletions(-)

--- a/lib/stackdepot.c~lib-stackdepot-rework-helpers-for-depot_alloc_stack
+++ a/lib/stackdepot.c
@@ -219,54 +219,43 @@ 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)
+/* Keeps the preallocated memory to be used for the next stack depot pool. */
+static void depot_keep_next_pool(void **prealloc)
 {
 	/*
-	 * If the next pool is already initialized or the maximum number of
+	 * If the next pool is already saved or the maximum number of
 	 * pools is reached, do not use the preallocated memory.
 	 */
 	if (!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;
+	/*
+	 * 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;
-	} 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.
-		 * smp_store_release pairs with smp_load_acquire in
-		 * stack_depot_save.
-		 */
-		smp_store_release(&next_pool_required, 0);
 	}
+
+	/*
+	 * At this point, either the next pool is kept or the maximum
+	 * number of pools is reached. In either case, take note that
+	 * keeping another pool is not required.
+	 * smp_store_release pairs with smp_load_acquire 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)
+/* Updates refences to the current and the next stack depot pools. */
+static bool depot_update_pools(size_t required_size, void **prealloc)
 {
-	struct stack_record *stack;
-	size_t required_size = DEPOT_STACK_RECORD_SIZE;
-
 	/* 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;
+			return false;
 		}
 
 		/*
@@ -276,9 +265,10 @@ depot_alloc_stack(unsigned long *entries
 		 */
 		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.
+		 * that the next pool needs to be initialized.
 		 * smp_store_release pairs with smp_load_acquire in
 		 * stack_depot_save.
 		 */
@@ -286,9 +276,30 @@ depot_alloc_stack(unsigned long *entries
 			smp_store_release(&next_pool_required, 1);
 	}
 
-	/* Assign the preallocated memory to a pool if required. */
+	/* Check if the current pool is not yet allocated. */
+	if (*prealloc && stack_pools[pool_index] == NULL) {
+		/* Use the preallocated memory for the current pool. */
+		stack_pools[pool_index] = *prealloc;
+		*prealloc = NULL;
+		return true;
+	}
+
+	/* Otherwise, try using the preallocated memory for the next pool. */
 	if (*prealloc)
-		depot_init_pool(prealloc);
+		depot_keep_next_pool(prealloc);
+	return true;
+}
+
+/* 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 = DEPOT_STACK_RECORD_SIZE;
+
+	/* Update current and next pools if required and possible. */
+	if (!depot_update_pools(required_size, prealloc))
+		return NULL;
 
 	/* Check if we have a pool to save the stack trace. */
 	if (stack_pools[pool_index] == NULL)
@@ -322,7 +333,7 @@ static struct stack_record *depot_fetch_
 	union handle_parts parts = { .handle = handle };
 	/*
 	 * READ_ONCE pairs with potential concurrent write in
-	 * depot_alloc_stack.
+	 * depot_update_pools.
 	 */
 	int pool_index_cached = READ_ONCE(pool_index);
 	void *pool;
@@ -421,8 +432,8 @@ depot_stack_handle_t __stack_depot_save(
 	 * 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.
 	 *
-	 * smp_load_acquire pairs with smp_store_release in depot_alloc_stack
-	 * and depot_init_pool.
+	 * smp_load_acquire pairs with smp_store_release in depot_update_pools
+	 * and depot_keep_next_pool.
 	 */
 	if (unlikely(can_alloc && smp_load_acquire(&next_pool_required))) {
 		/*
@@ -459,7 +470,7 @@ depot_stack_handle_t __stack_depot_save(
 		 * Stack depot already contains this stack trace, but let's
 		 * keep the preallocated memory for the future.
 		 */
-		depot_init_pool(&prealloc);
+		depot_keep_next_pool(&prealloc);
 	}
 
 	raw_spin_unlock_irqrestore(&pool_lock, flags);
_

Patches currently in -mm which might be from andreyknvl@google.com are

lib-stackdepot-check-disabled-flag-when-fetching.patch
lib-stackdepot-simplify-__stack_depot_save.patch
lib-stackdepot-drop-valid-bit-from-handles.patch
lib-stackdepot-add-depot_fetch_stack-helper.patch
lib-stackdepot-use-fixed-sized-slots-for-stack-records.patch
lib-stackdepot-fix-and-clean-up-atomic-annotations.patch
lib-stackdepot-rework-helpers-for-depot_alloc_stack.patch
lib-stackdepot-rename-next_pool_required-to-new_pool_required.patch
lib-stackdepot-store-next-pool-pointer-in-new_pool.patch
lib-stackdepot-store-free-stack-records-in-a-freelist.patch
lib-stackdepot-use-read-write-lock.patch
lib-stackdepot-use-list_head-for-stack-record-links.patch
kmsan-use-stack_depot_save-instead-of-__stack_depot_save.patch
lib-stackdepot-kasan-add-flags-to-__stack_depot_save-and-rename.patch
lib-stackdepot-add-refcount-for-records.patch
lib-stackdepot-allow-users-to-evict-stack-traces.patch
kasan-remove-atomic-accesses-to-stack-ring-entries.patch
kasan-check-object_size-in-kasan_complete_mode_report_info.patch
kasan-use-stack_depot_put-for-tag-based-modes.patch