gfs2: Use sb_start_intwrite in gfs2_ail_empty_gl

Commit 2e60d768 ("GFS2: update freeze code to use freeze/thaw_super
on all nodes") optimized away the sb_start_intwrite ... sb_end_intwrite
protection for the on-stack transactions in gfs2_ail_empty_gl with no
explanation.  I can't think of a valid reason for doing that, so revert
that change.  This simplifies the next commit.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glops.c

@@ -127,9 +127,12 @@ static int gfs2_ail_empty_gl(struct gfs2_glock *gl)
          * on the stack */
 	tr.tr_reserved = 1 + gfs2_struct2blk(sdp, tr.tr_revokes);
 	tr.tr_ip = _RET_IP_;
+	sb_start_intwrite(sdp->sd_vfs);
 	ret = gfs2_log_reserve(sdp, tr.tr_reserved);
-	if (ret < 0)
+	if (ret < 0) {
+		sb_end_intwrite(sdp->sd_vfs);
 		return ret;
+	}
 	WARN_ON_ONCE(current->journal_info);
 	current->journal_info = &tr;
 

fs/gfs2/trans.c

@@ -98,10 +98,9 @@ void gfs2_trans_end(struct gfs2_sbd *sdp)
 
 	if (!test_bit(TR_TOUCHED, &tr->tr_flags)) {
 		gfs2_log_release(sdp, tr->tr_reserved);
-		if (alloced) {
+		if (alloced)
 			gfs2_trans_free(sdp, tr);
-			sb_end_intwrite(sdp->sd_vfs);
-		}
+		sb_end_intwrite(sdp->sd_vfs);
 		return;
 	}
 
@@ -121,8 +120,7 @@ void gfs2_trans_end(struct gfs2_sbd *sdp)
 	if (sdp->sd_vfs->s_flags & SB_SYNCHRONOUS)
 		gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_NORMAL |
 			       GFS2_LFC_TRANS_END);
-	if (alloced)
-		sb_end_intwrite(sdp->sd_vfs);
+	sb_end_intwrite(sdp->sd_vfs);
 }
 
 static struct gfs2_bufdata *gfs2_alloc_bufdata(struct gfs2_glock *gl,