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>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index ecb1204468c3f2cef32af8b0190e3c9f691ebfa9..6e6df34d74f051df17e9a3b6079cadf2af49d8bb 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -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;