xfs: end sync buffer I/O properly on shutdown error

As of commit e339dd8d ("xfs: use sync buffer I/O for sync delwri
queue submission"), the delwri submission code uses sync buffer I/O
for sync delwri I/O. Instead of waiting on async I/O to unlock the
buffer, it uses the underlying sync I/O completion mechanism.

If delwri buffer submission fails due to a shutdown scenario, an
error is set on the buffer and buffer completion never occurs. This
can cause xfs_buf_delwri_submit() to deadlock waiting on a
completion event.

We could check the error state before waiting on such buffers, but
that doesn't serialize against the case of an error set via a racing
I/O completion. Instead, invoke I/O completion in the shutdown case
regardless of buffer I/O type.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_buf.c

@@ -1536,8 +1536,7 @@ __xfs_buf_submit(
 		xfs_buf_ioerror(bp, -EIO);
 		bp->b_flags &= ~XBF_DONE;
 		xfs_buf_stale(bp);
-		if (bp->b_flags & XBF_ASYNC)
-			xfs_buf_ioend(bp);
+		xfs_buf_ioend(bp);
 		return -EIO;
 	}