[PATCH v2 07/19] lib/stackdepot: rework helpers for depot_alloc_stack

andrey.konovalov
2023-09-13T17:16:00Z

From: Andrey Konovalov <andreyknvl@google.com>

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.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
lib/stackdepot.c | 87 +++++++++++++++++++++++++++---------------------
1 file changed, 49 insertions(+), 38 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index babd453261f0..e85b658be050 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -219,54 +219,43 @@ int stack_depot_init(void)
}
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, int size, u32 hash, void **prealloc)
*/
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, int size, u32 hash, void **prealloc)
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_stack(depot_stack_handle_t handle)
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(unsigned long *entries,
* 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(unsigned long *entries,
* 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);
--
2.25.1