[PATCH 4.18 139/197] btrfs: lift uuid_mutex to callers of btrfs_open_devices

[Greg Kroah-Hartman]

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

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

From: David Sterba <dsterba@xxxxxxxx>

[ Upstream commit f5194e34cabaddd348a90f950e0a8188dd26cdc0 ]

Prepartory work to fix race between mount and device scan.

The callers will have to manage the critical section, eg. mount wants to
scan and then call btrfs_open_devices without the ioctl scan walking in
and modifying the fs devices in the meantime.

Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/btrfs/super.c   |    2 ++
 fs/btrfs/volumes.c |    4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1565,7 +1565,9 @@ static struct dentry *btrfs_mount_root(s
 		goto error_fs_info;
 	}
 
+	mutex_lock(&uuid_mutex);
 	error = btrfs_open_devices(fs_devices, mode, fs_type);
+	mutex_unlock(&uuid_mutex);
 	if (error)
 		goto error_fs_info;
 
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1146,7 +1146,8 @@ int btrfs_open_devices(struct btrfs_fs_d
 {
 	int ret;
 
-	mutex_lock(&uuid_mutex);
+	lockdep_assert_held(&uuid_mutex);
+
 	mutex_lock(&fs_devices->device_list_mutex);
 	if (fs_devices->opened) {
 		fs_devices->opened++;
@@ -1156,7 +1157,6 @@ int btrfs_open_devices(struct btrfs_fs_d
 		ret = open_fs_devices(fs_devices, flags, holder);
 	}
 	mutex_unlock(&fs_devices->device_list_mutex);
-	mutex_unlock(&uuid_mutex);
 
 	return ret;
 }