On 06/21/2018 01:51 AM, David Sterba wrote:
Commit 542c5908abfe84f7b4c1 ("btrfs: replace uuid_mutex by
device_list_mutex in btrfs_open_devices") switched to device_list_mutex
as we need that for the device list traversal, but we also need
uuid_mutex to protect access to fs_devices::opened to be consistent with
other users of that item.

CC: Anand Jain <anand.j...@oracle.com>
Signed-off-by: David Sterba <dste...@suse.com>

I am optimize the uuid_mutex for fsids concurrency on top these set of patches, so.

 Reviewed-by: Anand Jain <anand.j...@oracle.com>

Thanks, Anand

---
  fs/btrfs/volumes.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e034ad9e23b4..1da162928d1a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1146,6 +1146,7 @@ int btrfs_open_devices(struct btrfs_fs_devices 
*fs_devices,
  {
        int ret;
+ mutex_lock(&uuid_mutex);
        mutex_lock(&fs_devices->device_list_mutex);
        if (fs_devices->opened) {
                fs_devices->opened++;
@@ -1155,6 +1156,7 @@ int btrfs_open_devices(struct btrfs_fs_devices 
*fs_devices,
                ret = open_fs_devices(fs_devices, flags, holder);
        }
        mutex_unlock(&fs_devices->device_list_mutex);
+       mutex_unlock(&uuid_mutex);
return ret;
  }

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