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

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.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
(cherry picked from commit 5e6ecb362bd5950a3d8ce19c32829e4f8c7917d9)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 89f08c469a3730bddf0e581800077e1cf412a4f4..d0b16deed8c373d6cdc49505450902762915c280 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3071,8 +3071,12 @@ 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;