[PATCH v2 04/19] lib/stackdepot: add depot_fetch_stack helper

andrey.konovalov
2023-09-13T17:15:05Z

From: Andrey Konovalov <andreyknvl@google.com>

Add a helper depot_fetch_stack function that fetches the pointer to
a stack record.

With this change, all static depot_* functions now operate on stack pools
and the exported stack_depot_* functions operate on the hash table.

Reviewed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v1->v2:
- Minor comment fix as suggested by Alexander.
---
lib/stackdepot.c | 45 ++++++++++++++++++++++++++++-----------------
1 file changed, 28 insertions(+), 17 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 482eac40791e..9a004f15f59d 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -304,6 +304,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
stack->handle.extra = 0;
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.
@@ -313,6 +314,32 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
return stack;
}

+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().
+ */
+ int pool_index_cached = READ_ONCE(pool_index);
+ void *pool;
+ size_t offset = parts.offset << DEPOT_STACK_ALIGN;
+ struct stack_record *stack;
+
+ 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 NULL;
+ }
+
+ pool = stack_pools[parts.pool_index];
+ if (!pool)
+ return NULL;
+
+ stack = pool + offset;
+ return stack;
+}
+
/* Calculates the hash for a stack. */
static inline u32 hash_stack(unsigned long *entries, unsigned int size)
{
@@ -456,14 +483,6 @@ 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;
@@ -476,15 +495,7 @@ unsigned int stack_depot_fetch(depot_stack_handle_t 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;
+ stack = depot_fetch_stack(handle);

*entries = stack->entries;
return stack->size;
--
2.25.1