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, 1 insertions, 1 deletions

diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
index fc821aa446f0..21605b03f511 100644
--- a/fs/btrfs/print-tree.c
+++ b/fs/btrfs/print-tree.c
@@ -223,7 +223,7 @@ static void print_eb_refs_lock(const struct extent_buffer *eb)
 {
 #ifdef CONFIG_BTRFS_DEBUG
 	btrfs_info(eb->fs_info, "refs %u lock_owner %u current %u",
-		   atomic_read(&eb->refs), eb->lock_owner, current->pid);
+		   refcount_read(&eb->refs), eb->lock_owner, current->pid);
 #endif
 }