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 <[email protected]> (Moved the checks above the position checks /Jens) Signed-off-by: Jens Axboe <[email protected]>
vbatts · Sep 25, 2010 · f281fb5 · f281fb5
1 parent a850ea3
commit f281fb5
Showing 1 changed file with 12 additions and 0 deletions.
diff --git a/block/blk-merge.c b/block/blk-merge.c
@@ -361,6 +361,18 @@ static int attempt_merge(struct request_queue *q, struct request *req,
 	if (!rq_mergeable(req) || !rq_mergeable(next))
 		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
 	 */