GFS2: Clean up log flush header writing

We already send both a pre and post flush to the block device
when writing a journal header. There is no need to wait for
the previous I/O specifically when we do this, unless we've
turned "barriers" off.

As a side effect, this also cleans up the code path for flushing
the journal and makes it more readable.
Signed-off-by: NSteven Whitehouse <swhiteho@redhat.com>

fs/gfs2/log.c

@@ -491,66 +491,8 @@ static void log_pull_tail(struct gfs2_sbd *sdp, unsigned int new_tail)
 	sdp->sd_log_tail = new_tail;
 }
 
-/**
- * log_write_header - Get and initialize a journal header buffer
- * @sdp: The GFS2 superblock
- *
- * Returns: the initialized log buffer descriptor
- */
 
-static void log_write_header(struct gfs2_sbd *sdp, u32 flags, int pull)
-{
-	u64 blkno = gfs2_log_bmap(sdp, sdp->sd_log_flush_head);
-	struct buffer_head *bh;
-	struct gfs2_log_header *lh;
-	unsigned int tail;
-	u32 hash;
-
-	bh = sb_getblk(sdp->sd_vfs, blkno);
-	lock_buffer(bh);
-	memset(bh->b_data, 0, bh->b_size);
-	set_buffer_uptodate(bh);
-	clear_buffer_dirty(bh);
-
-	gfs2_ail1_empty(sdp);
-	tail = current_tail(sdp);
-
-	lh = (struct gfs2_log_header *)bh->b_data;
-	memset(lh, 0, sizeof(struct gfs2_log_header));
-	lh->lh_header.mh_magic = cpu_to_be32(GFS2_MAGIC);
-	lh->lh_header.mh_type = cpu_to_be32(GFS2_METATYPE_LH);
-	lh->lh_header.__pad0 = cpu_to_be64(0);
-	lh->lh_header.mh_format = cpu_to_be32(GFS2_FORMAT_LH);
-	lh->lh_header.mh_jid = cpu_to_be32(sdp->sd_jdesc->jd_jid);
-	lh->lh_sequence = cpu_to_be64(sdp->sd_log_sequence++);
-	lh->lh_flags = cpu_to_be32(flags);
-	lh->lh_tail = cpu_to_be32(tail);
-	lh->lh_blkno = cpu_to_be32(sdp->sd_log_flush_head);
-	hash = gfs2_disk_hash(bh->b_data, sizeof(struct gfs2_log_header));
-	lh->lh_hash = cpu_to_be32(hash);
-
-	bh->b_end_io = end_buffer_write_sync;
-	get_bh(bh);
-	if (test_bit(SDF_NOBARRIERS, &sdp->sd_flags))
-		submit_bh(WRITE_SYNC | REQ_META | REQ_PRIO, bh);
-	else
-		submit_bh(WRITE_FLUSH_FUA | REQ_META, bh);
-	wait_on_buffer(bh);
-
-	if (!buffer_uptodate(bh))
-		gfs2_io_error_bh(sdp, bh);
-	brelse(bh);
-
-	if (sdp->sd_log_tail != tail)
-		log_pull_tail(sdp, tail);
-	else
-		gfs2_assert_withdraw(sdp, !pull);
-
-	sdp->sd_log_idle = (tail == sdp->sd_log_flush_head);
-	gfs2_log_incr_head(sdp);
-}
-
-static void log_flush_commit(struct gfs2_sbd *sdp)
+static void log_flush_wait(struct gfs2_sbd *sdp)
 {
 	DEFINE_WAIT(wait);
 
@@ -563,8 +505,6 @@ static void log_flush_commit(struct gfs2_sbd *sdp)
 		} while(atomic_read(&sdp->sd_log_in_flight));
 		finish_wait(&sdp->sd_log_flush_wait, &wait);
 	}
-
-	log_write_header(sdp, 0, 0);
 }
 
 static int bd_cmp(void *priv, struct list_head *a, struct list_head *b)
@@ -633,6 +573,68 @@ static void gfs2_ordered_wait(struct gfs2_sbd *sdp)
 	gfs2_log_unlock(sdp);
 }
 
+/**
+ * log_write_header - Get and initialize a journal header buffer
+ * @sdp: The GFS2 superblock
+ *
+ * Returns: the initialized log buffer descriptor
+ */
+
+static void log_write_header(struct gfs2_sbd *sdp, u32 flags, int pull)
+{
+	u64 blkno = gfs2_log_bmap(sdp, sdp->sd_log_flush_head);
+	struct buffer_head *bh;
+	struct gfs2_log_header *lh;
+	unsigned int tail;
+	u32 hash;
+
+	bh = sb_getblk(sdp->sd_vfs, blkno);
+	lock_buffer(bh);
+	memset(bh->b_data, 0, bh->b_size);
+	set_buffer_uptodate(bh);
+	clear_buffer_dirty(bh);
+
+	gfs2_ail1_empty(sdp);
+	tail = current_tail(sdp);
+
+	lh = (struct gfs2_log_header *)bh->b_data;
+	memset(lh, 0, sizeof(struct gfs2_log_header));
+	lh->lh_header.mh_magic = cpu_to_be32(GFS2_MAGIC);
+	lh->lh_header.mh_type = cpu_to_be32(GFS2_METATYPE_LH);
+	lh->lh_header.__pad0 = cpu_to_be64(0);
+	lh->lh_header.mh_format = cpu_to_be32(GFS2_FORMAT_LH);
+	lh->lh_header.mh_jid = cpu_to_be32(sdp->sd_jdesc->jd_jid);
+	lh->lh_sequence = cpu_to_be64(sdp->sd_log_sequence++);
+	lh->lh_flags = cpu_to_be32(flags);
+	lh->lh_tail = cpu_to_be32(tail);
+	lh->lh_blkno = cpu_to_be32(sdp->sd_log_flush_head);
+	hash = gfs2_disk_hash(bh->b_data, sizeof(struct gfs2_log_header));
+	lh->lh_hash = cpu_to_be32(hash);
+
+	bh->b_end_io = end_buffer_write_sync;
+	get_bh(bh);
+	if (test_bit(SDF_NOBARRIERS, &sdp->sd_flags)) {
+		gfs2_ordered_wait(sdp);
+		log_flush_wait(sdp);
+		submit_bh(WRITE_SYNC | REQ_META | REQ_PRIO, bh);
+	} else {
+		submit_bh(WRITE_FLUSH_FUA | REQ_META, bh);
+	}
+	wait_on_buffer(bh);
+
+	if (!buffer_uptodate(bh))
+		gfs2_io_error_bh(sdp, bh);
+	brelse(bh);
+
+	if (sdp->sd_log_tail != tail)
+		log_pull_tail(sdp, tail);
+	else
+		gfs2_assert_withdraw(sdp, !pull);
+
+	sdp->sd_log_idle = (tail == sdp->sd_log_flush_head);
+	gfs2_log_incr_head(sdp);
+}
+
 /**
  * gfs2_log_flush - flush incore transaction(s)
  * @sdp: the filesystem
@@ -676,11 +678,10 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl)
 
 	gfs2_ordered_write(sdp);
 	lops_before_commit(sdp);
-	gfs2_ordered_wait(sdp);
 
-	if (sdp->sd_log_head != sdp->sd_log_flush_head)
-		log_flush_commit(sdp);
-	else if (sdp->sd_log_tail != current_tail(sdp) && !sdp->sd_log_idle){
+	if (sdp->sd_log_head != sdp->sd_log_flush_head) {
+		log_write_header(sdp, 0, 0);
+	} else if (sdp->sd_log_tail != current_tail(sdp) && !sdp->sd_log_idle){
 		gfs2_log_lock(sdp);
 		atomic_dec(&sdp->sd_log_blks_free); /* Adjust for unreserved buffer */
 		trace_gfs2_log_blocks(sdp, -1);