Re: [PATCH 4/7] btrfs: lift uuid_mutex to callers of btrfs_open_devices

[Anand Jain]

On 06/21/2018 01:51 AM, David Sterba wrote:

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.

Signed-off-by: David Sterba <dste...@suse.com>

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

Thanks, Anand

---
  fs/btrfs/super.c   | 2 ++
  fs/btrfs/volumes.c | 4 ++--
  2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 735402ed3154..ee82d02f5453 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1569,7 +1569,9 @@ static struct dentry *btrfs_mount_root(struct 
file_system_type *fs_type,
                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;

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c

index 958bfe1a725c..5336d9832ba4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1145,7 +1145,8 @@ int btrfs_open_devices(struct btrfs_fs_devices 
*fs_devices,
  {
        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++;
@@ -1155,7 +1156,6 @@ 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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