btrfs: print name and pid when device scanning processes race

There is a race between systemd and mount, as both of them try to register
the device in the kernel. When systemd loses the race, it prints the
following message:

  BTRFS error: device /dev/sdb7 belongs to fsid 1b3bacbf-14db-49c9-a3ef-547998aacc4e, and the fs is already mounted.

The 'btrfs dev scan' registers one device at a time, so there is no way
for the mount thread to wait in the kernel for all the devices to have
registered as it won't know if all the devices are discovered.

For now, improve the error log by printing the command name and process
ID along with the error message.

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

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8af0e54099c2dee7b13d9ded4fc8531aa6f56fad..89410a480293b7081e9a9195d1ec5c9ab07f1691 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -851,8 +851,9 @@ static noinline struct btrfs_device *device_list_add(const char *path,
 
                if (fs_devices->opened) {
                        btrfs_err(NULL,
-               "device %s belongs to fsid %pU, and the fs is already mounted",
-                                 path, fs_devices->fsid);
+"device %s belongs to fsid %pU, and the fs is already mounted, scanned by %s (%d)",
+                                 path, fs_devices->fsid, current->comm,
+                                 task_pid_nr(current));
                        mutex_unlock(&fs_devices->device_list_mutex);
                        return ERR_PTR(-EBUSY);
                }