gfs2: bypass log flush if the journal is not live

Patch fe3e3976 ("gfs2: Rework the log space allocation logic")
changed gfs2_log_flush to reserve a set of journal blocks in case no
transaction is active.  However, gfs2_log_flush also gets called in
cases where we don't have an active journal, for example, for spectator
mounts.  In that case, trying to reserve blocks would sleep forever, but
we want gfs2_log_flush to be a no-op instead.

Fixes: fe3e3976 ("gfs2: Rework the log space allocation logic")
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/log.c

@@ -1036,7 +1036,7 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
 	 * Do this check while holding the log_flush_lock to prevent new
 	 * buffers from being added to the ail via gfs2_pin()
 	 */
-	if (gfs2_withdrawn(sdp))
+	if (gfs2_withdrawn(sdp) || !test_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags))
 		goto out;
 
 	/* Log might have been flushed while we waited for the flush lock */