From f281fb5fe54e15a7ab802945e42f8e24fceb56b2 Mon Sep 17 00:00:00 2001 From: Adrian Hunter <adrian.hunter@nokia.com> Date: Sat, 25 Sep 2010 12:42:55 +0200 Subject: [PATCH] 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> --- block/blk-merge.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/block/blk-merge.c b/block/blk-merge.c index 3b0cd4249671d..eafc94f68d79f 100644 --- 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 */ -- GitLab