btrfs: use refcount_t type for the extent buffer reference counter

[ Upstream commit b769777d927af168b1389388392bfd7dc4e38399 ]

Instead of using a bare atomic, use the refcount_t type, which despite
being a structure that contains only an atomic, has an API that checks
for underflows and other hazards. This doesn't change the size of the
extent_buffer structure.

This removes the need to do things like this:

    WARN_ON(atomic_read(&eb->refs) == 0);
    if (atomic_dec_and_test(&eb->refs)) {
        (...)
    }

And do just:

    if (refcount_dec_and_test(&eb->refs)) {
        (...)
    }

Since refcount_dec_and_test() already triggers a warning when we decrement
a ref count that has a value of 0 (or below zero).

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: ad580dfa388f ("btrfs: fix subpage deadlock in try_release_subpage_extent_buffer()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 7241229d218b..afc05e406689 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2747,7 +2747,7 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
 	level = btrfs_header_level(log->node);
 	orig_level = level;
 	path->nodes[level] = log->node;
-	atomic_inc(&log->node->refs);
+	refcount_inc(&log->node->refs);
 	path->slots[level] = 0;
 
 	while (1) {
@@ -3711,7 +3711,7 @@ static int clone_leaf(struct btrfs_path *path, struct btrfs_log_ctx *ctx)
 	 * Add extra ref to scratch eb so that it is not freed when callers
 	 * release the path, so we can reuse it later if needed.
 	 */
-	atomic_inc(&ctx->scratch_eb->refs);
+	refcount_inc(&ctx->scratch_eb->refs);
 
 	return 0;
 }