wake up s_wait_unfrozen when ->freeze_fs fails

commit e1616300a20c80396109c1cf013ba9a36055a3da upstream.

dd slept infinitely when fsfeeze failed because of EIO.
To fix this problem, if ->freeze_fs fails, freeze_super() wakes up
the tasks waiting for the filesystem to become unfrozen.

When s_frozen isn't SB_UNFROZEN in __generic_file_aio_write(),
the function sleeps until FITHAW ioctl wakes up s_wait_unfrozen.

However, if ->freeze_fs fails, s_frozen is set to SB_UNFROZEN and then
freeze_super() returns an error number. In this case, FITHAW ioctl returns
EINVAL because s_frozen is already SB_UNFROZEN. There is no way to wake up
s_wait_unfrozen, so __generic_file_aio_write() sleeps infinitely.

Signed-off-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/super.c b/fs/super.c
index ab3d672..caf4dfa 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1009,6 +1009,8 @@ int freeze_super(struct super_block *sb)
 			printk(KERN_ERR
 				"VFS:Filesystem freeze failed\n");
 			sb->s_frozen = SB_UNFROZEN;
+			smp_wmb();
+			wake_up(&sb->s_wait_unfrozen);
 			deactivate_locked_super(sb);
 			return ret;
 		}