btrfs: dev-replace: go back to suspend state if another EXCL_OP is running

In a secnario where balance and replace co-exists as below,

  - start balance
  - pause balance
  - start replace
  - reboot

and when system restarts, balance resumes first. Then the replace is
attempted to restart but will fail as the EXCL_OP lock is already held
by the balance. If so place the replace state back to
BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED state.

Fixes: 010a47bd ("btrfs: add proper safety check before resuming dev-replace")
CC: stable@vger.kernel.org # 4.18+
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/dev-replace.c

@@ -903,6 +903,10 @@ int btrfs_resume_dev_replace_async(struct btrfs_fs_info *fs_info)
 	 * dev-replace to start anyway.
 	 */
 	if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
+		btrfs_dev_replace_write_lock(dev_replace);
+		dev_replace->replace_state =
+					BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED;
+		btrfs_dev_replace_write_unlock(dev_replace);
 		btrfs_info(fs_info,
 		"cannot resume dev-replace, other exclusive operation running");
 		return 0;