block: fix bug with inserting flush requests as sort/merge

With the introduction of the on-stack plugging, we would assume
that any request being inserted was a normal file system request.
As flush/fua requires a special insert mode, this caused problems.

Fix this up by checking for this in flush_plug_list() and use
the appropriate insert mechanism.

Big thanks goes to Markus Tripplesdorf for tirelessly testing
patches, and to Sergey Senozhatsky for helping find the real
issue.

Reported-by: Markus Tripplesdorf <markus@trippelsdorf.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 59b5c00c0126..64e96ee1d6af 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2702,7 +2702,10 @@ static void flush_plug_list(struct blk_plug *plug)
                 /*
                  * rq is already accounted, so use raw insert
                  */
-                __elv_add_request(q, rq, ELEVATOR_INSERT_SORT_MERGE);
+                if (rq->cmd_flags & (REQ_FLUSH | REQ_FUA))
+                        __elv_add_request(q, rq, ELEVATOR_INSERT_FLUSH);
+                else
+                        __elv_add_request(q, rq, ELEVATOR_INSERT_SORT_MERGE);
         }
 
         if (q) {