[PATCH] btrfs: Fix a bug in try_release_subpage_extent_buffer()

[Bart Van Assche <bvanassche@acm.org>]

Call rcu_read_lock() before exiting the loop in
try_release_subpage_extent_buffer() because there is a rcu_read_unlock()
call past the loop. This has been detected by the Clang thread-safety
analyzer. Compile-tested only.

Cc: Boris Burkov <boris@bur.io>
Cc: Qu Wenruo <wqu@suse.com>
Cc: Leo Martins <loemra.dev@gmail.com>
Cc: Chris Mason <clm@fb.com>
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Fixes: ad580dfa388f ("btrfs: fix subpage deadlock in try_release_subpage_extent_buffer()")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 fs/btrfs/extent_io.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 744a1fff6eef..5f97a3d2a8d7 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4507,6 +4507,7 @@ static int try_release_subpage_extent_buffer(struct folio *folio)
 		 */
 		if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
 			spin_unlock(&eb->refs_lock);
+			rcu_read_lock();
 			break;
 		}