3.11.10.2 -stable review patch.  If anyone has any objections, please let me 
know.

------------------

From: David Sterba <[email protected]>

commit e43f998e47bae27e37e159915625e8d4b130153b upstream.

If btrfs_ioctl_snap_destroy blocks on the mutex and the process is
killed, mnt_write count is unbalanced and leads to unmountable
filesystem.

Signed-off-by: David Sterba <[email protected]>
Signed-off-by: Chris Mason <[email protected]>
Signed-off-by: Luis Henriques <[email protected]>
---
 fs/btrfs/ioctl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 9877a2a..6074a8e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2099,7 +2099,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file 
*file,
 
        err = mutex_lock_killable_nested(&dir->i_mutex, I_MUTEX_PARENT);
        if (err == -EINTR)
-               goto out;
+               goto out_drop_write;
        dentry = lookup_one_len(vol_args->name, parent, namelen);
        if (IS_ERR(dentry)) {
                err = PTR_ERR(dentry);
@@ -2241,6 +2241,7 @@ out_dput:
        dput(dentry);
 out_unlock_dir:
        mutex_unlock(&dir->i_mutex);
+out_drop_write:
        mnt_drop_write_file(file);
 out:
        kfree(vol_args);
-- 
1.8.3.2

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