block: prevent merges of discard and write requests
Add logic to prevent two I/O requests being merged if
only one of them is a discard. Ditto secure discard.
Without this fix, it is possible for write requests
to transform into discard requests. For example:
Submit bio 1 to discard 8 sectors from sector n
Submit bio 2 to write 8 sectors from sector n + 16
Submit bio 3 to write 8 sectors from sector n + 8
Bio 1 becomes request 1. Bio 2 becomes request 2.
Bio 3 is merged with request 2, and then subsequently
request 2 is merged with request 1 resulting in just
one I/O request which discards all 24 sectors.
Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
(Moved the checks above the position checks /Jens)
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 3b0cd42..eafc94f 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -362,6 +362,18 @@
return 0;
/*
+ * Don't merge file system requests and discard requests
+ */
+ if ((req->cmd_flags & REQ_DISCARD) != (next->cmd_flags & REQ_DISCARD))
+ return 0;
+
+ /*
+ * Don't merge discard requests and secure discard requests
+ */
+ if ((req->cmd_flags & REQ_SECURE) != (next->cmd_flags & REQ_SECURE))
+ return 0;
+
+ /*
* not contiguous
*/
if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))