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

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>
Acked-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 41 insertions, 34 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 2fc269f69726..24b702d649a9 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -293,7 +293,7 @@ void elv_requeue_request(request_queue_t *q, struct request *rq)
 
         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)
@@ -310,41 +310,11 @@ static void elv_drain_elevator(request_queue_t *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;
 
-        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) {
@@ -425,6 +395,42 @@ void __elv_add_request(request_queue_t *q, struct request *rq, int where,
         }
 }
 
+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 ee5ed98db4cd..03d9c82b0fe7 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -454,7 +454,7 @@ static void queue_flush(request_queue_t *q, unsigned which)
         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,
@@ -490,7 +490,7 @@ static inline struct request *start_ordered(request_queue_t *q,
         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 23fe746a1d51..18cf1f3e1184 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 *);