btrfs: reduce uuid_mutex critical section while scanning devices

The generic block device lookup or cleanup does not need the uuid mutex,
that's only for the device_list_add.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index ebc8176..c1d09da 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1232,31 +1232,29 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
         */
        bytenr = btrfs_sb_offset(0);
        flags |= FMODE_EXCL;
-       mutex_lock(&uuid_mutex);
 
        bdev = blkdev_get_by_path(path, flags, holder);
-       if (IS_ERR(bdev)) {
-               ret = PTR_ERR(bdev);
-               goto error;
-       }
+       if (IS_ERR(bdev))
+               return PTR_ERR(bdev);
 
        if (btrfs_read_disk_super(bdev, bytenr, &page, &disk_super)) {
                ret = -EINVAL;
                goto error_bdev_put;
        }
 
+       mutex_lock(&uuid_mutex);
        device = device_list_add(path, disk_super);
        if (IS_ERR(device))
                ret = PTR_ERR(device);
        else
                *fs_devices_ret = device->fs_devices;
+       mutex_unlock(&uuid_mutex);
 
        btrfs_release_disk_super(page);
 
 error_bdev_put:
        blkdev_put(bdev, flags);
-error:
-       mutex_unlock(&uuid_mutex);
+
        return ret;
 }