[PATCH 2/2] block: implement elv_insert and use it (fix ordcolor flipping bug)

[Tejun Heo <htejun@gmail.com>]

q->ordcolor must only be flipped on initial queueing of a hardbarrier
request.  Constructing ordered sequence and requeueing used to pass
through __elv_add_request() which flips q->ordcolor when it sees a
barrier request.  This patch separates out elv_insert() from
__elv_add_request() and uses elv_insert() when constructing ordered
sequence and requeueing.  elv_insert() inserts the given request at
the specified position and does nothing else.

Signed-off-by: Tejun Heo <htejun@gmail.com>

---

 block/elevator.c         |   70 +++++++++++++++++++++++++---------------------
 block/ll_rw_blk.c        |    4 +--
 include/linux/elevator.h |    1 +
 3 files changed, 41 insertions(+), 34 deletions(-)

c48805c420fd95f32b75b945c4011e5d5220188e
diff --git a/block/elevator.c b/block/elevator.c
index 4c0fe1c..86c62b2 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -304,7 +304,7 @@ void elv_requeue_request(request_queue_t
 
 	rq->flags &= ~REQ_STARTED;
 
-	__elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE, 0);
+	elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 }
 
 static void elv_drain_elevator(request_queue_t *q)
@@ -321,43 +321,13 @@ static void elv_drain_elevator(request_q
 	}
 }
 
-void __elv_add_request(request_queue_t *q, struct request *rq, int where,
-		       int plug)
+void elv_insert(request_queue_t *q, struct request *rq, int where)
 {
 	struct list_head *pos;
 	unsigned ordseq;
 
 	blk_add_trace_rq(q, rq, BLK_TA_INSERT);
 
-	if (q->ordcolor)
-		rq->flags |= REQ_ORDERED_COLOR;
-
-	if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
-		/*
-		 * toggle ordered color
-		 */
-		if (blk_barrier_rq(rq))
-			q->ordcolor ^= 1;
-
-		/*
-		 * barriers implicitly indicate back insertion
-		 */
-		if (where == ELEVATOR_INSERT_SORT)
-			where = ELEVATOR_INSERT_BACK;
-
-		/*
-		 * this request is scheduling boundary, update end_sector
-		 */
-		if (blk_fs_request(rq)) {
-			q->end_sector = rq_end_sector(rq);
-			q->boundary_rq = rq;
-		}
-	} else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
-		where = ELEVATOR_INSERT_BACK;
-
-	if (plug)
-		blk_plug_device(q);
-
 	rq->q = q;
 
 	switch (where) {
@@ -438,6 +408,42 @@ void __elv_add_request(request_queue_t *
 	}
 }
 
+void __elv_add_request(request_queue_t *q, struct request *rq, int where,
+		       int plug)
+{
+	if (q->ordcolor)
+		rq->flags |= REQ_ORDERED_COLOR;
+
+	if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
+		/*
+		 * toggle ordered color
+		 */
+		if (blk_barrier_rq(rq))
+			q->ordcolor ^= 1;
+
+		/*
+		 * barriers implicitly indicate back insertion
+		 */
+		if (where == ELEVATOR_INSERT_SORT)
+			where = ELEVATOR_INSERT_BACK;
+
+		/*
+		 * this request is scheduling boundary, update
+		 * end_sector
+		 */
+		if (blk_fs_request(rq)) {
+			q->end_sector = rq_end_sector(rq);
+			q->boundary_rq = rq;
+		}
+	} else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
+		where = ELEVATOR_INSERT_BACK;
+
+	if (plug)
+		blk_plug_device(q);
+
+	elv_insert(q, rq, where);
+}
+
 void elv_add_request(request_queue_t *q, struct request *rq, int where,
 		     int plug)
 {
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 83687f9..23c1148 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -453,7 +453,7 @@ static void queue_flush(request_queue_t 
 	rq->end_io = end_io;
 	q->prepare_flush_fn(q, rq);
 
-	__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
+	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 }
 
 static inline struct request *start_ordered(request_queue_t *q,
@@ -489,7 +489,7 @@ static inline struct request *start_orde
 	else
 		q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
 
-	__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
+	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
 
 	if (q->ordered & QUEUE_ORDERED_PREFLUSH) {
 		queue_flush(q, QUEUE_ORDERED_PREFLUSH);
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 23fe746..18cf1f3 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -82,6 +82,7 @@ struct elevator_queue
 extern void elv_dispatch_sort(request_queue_t *, struct request *);
 extern void elv_add_request(request_queue_t *, struct request *, int, int);
 extern void __elv_add_request(request_queue_t *, struct request *, int, int);
+extern void elv_insert(request_queue_t *, struct request *, int);
 extern int elv_merge(request_queue_t *, struct request **, struct bio *);
 extern void elv_merge_requests(request_queue_t *, struct request *,
 			       struct request *);
-- 
1.0.6