Btrfs: fix double range unlock of hole region when reading page

From: Filipe Manana <[email protected]>

If when reading a page we find a hole and our caller had already locked the range (bio flags has the bit EXTENT_BIO_PARENT_LOCKED set), we end up unlocking the hole's range and then later our caller unlocks it again, which might have already been locked by some other task once the first unlock happened.

Currently this can only happen during a call to the extent_same ioctl, as it's the only caller of __do_readpage() that sets the bit EXTENT_BIO_PARENT_LOCKED for bio flags.

Fix this by leaving the unlock exclusively to the caller.

---
 fs/btrfs/extent_io.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index ecb1204..6e6df34 100644
@@ -3070,8 +3070,12 @@ static int __do_readpage(struct extent_io_tree *tree,
 
 			set_extent_uptodate(tree, cur, cur + iosize - 1,
 					    &cached, GFP_NOFS);
-			unlock_extent_cached(tree, cur, cur + iosize - 1,
-			                     &cached, GFP_NOFS);
+			if (parent_locked)
+				free_extent_state(cached);
+			else
+				unlock_extent_cached(tree, cur,
+						     cur + iosize - 1,
+						     &cached, GFP_NOFS);
 			cur = cur + iosize;
 			pg_offset += iosize;
 			continue;

2.1.3