btrfs: Init io_lock after cloning btrfs device struct

__btrfs_close_devices() clones btrfs device structs with
memcpy(). Some of the fields in the clone are reinitialized, but it's
missing to init io_lock. In mainline this goes unnoticed, but on RT it
leaves the plist pointing to the original about to be freed lock
struct.

Initialize io_lock after cloning, so no references to the original
struct are left.

Reported-and-tested-by: Mike Galbraith <efault@gmx.de>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 7992dc4ea4ccecf1cc9d771dc72edb1d0455e16a..5d6010ba8b7eb3fc5121fc5e29a738c175c45865 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -650,6 +650,7 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
                new_device->writeable = 0;
                new_device->in_fs_metadata = 0;
                new_device->can_discard = 0;
+               spin_lock_init(&new_device->io_lock);
                list_replace_rcu(&device->dev_list, &new_device->dev_list);
 
                call_rcu(&device->rcu, free_device);