On Thu, Feb 15, 2024 at 10:58 PM Oscar Salvador <osalvador@xxxxxxx> wrote:
>
> The very first entry of stack_record gets a handle of 0, but this is wrong
> because stackdepot treats a 0-handle as a non-valid one.
> E.g: See the check in stack_depot_fetch()
>
> Fix this by adding and offset of 1.
>
> This bug has been lurking since the very beginning of stackdepot,
> but no one really cared as it seems.
> Because of that I am not adding a Fixes tag.
>
> Co-developed-by: Marco Elver <elver@xxxxxxxxxx>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> lib/stackdepot.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 4a7055a63d9f..c043a4186bc5 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -45,15 +45,16 @@
> #define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
> STACK_DEPOT_EXTRA_BITS)
> #define DEPOT_POOLS_CAP 8192
> +/* The pool_index is offset by 1 so the first record does not have a 0 handle. */
> #define DEPOT_MAX_POOLS \
> - (((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
> - (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)
> + (((1LL << (DEPOT_POOL_INDEX_BITS)) - 1 < DEPOT_POOLS_CAP) ? \
> + (1LL << (DEPOT_POOL_INDEX_BITS)) - 1 : DEPOT_POOLS_CAP)
>
> /* Compact structure that stores a reference to a stack. */
> union handle_parts {
> depot_stack_handle_t handle;
> struct {
> - u32 pool_index : DEPOT_POOL_INDEX_BITS;
> + u32 pool_index : DEPOT_POOL_INDEX_BITS; /* pool_index is offset by 1 */
> u32 offset : DEPOT_OFFSET_BITS;
> u32 extra : STACK_DEPOT_EXTRA_BITS;
> };
> @@ -372,7 +373,7 @@ static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
> stack = current_pool + pool_offset;
>
> /* Pre-initialize handle once. */
> - stack->handle.pool_index = pool_index;
> + stack->handle.pool_index = pool_index + 1;
> stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
> stack->handle.extra = 0;
> INIT_LIST_HEAD(&stack->hash_list);
> @@ -483,18 +484,19 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
> const int pools_num_cached = READ_ONCE(pools_num);
> union handle_parts parts = { .handle = handle };
> void *pool;
> + u32 pool_index = parts.pool_index - 1;
> size_t offset = parts.offset << DEPOT_STACK_ALIGN;
> struct stack_record *stack;
>
> lockdep_assert_not_held(&pool_lock);
>
> - if (parts.pool_index > pools_num_cached) {
> + if (pool_index > pools_num_cached) {
> WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
> - parts.pool_index, pools_num_cached, handle);
> + pool_index, pools_num_cached, handle);
> return NULL;
> }
>
> - pool = stack_pools[parts.pool_index];
> + pool = stack_pools[pool_index];
> if (WARN_ON(!pool))
> return NULL;
>
> --
> 2.43.0
>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
