From f281fb5fe54e15a7ab802945e42f8e24fceb56b2 Mon Sep 17 00:00:00 2001 From: Adrian Hunter Date: Sat, 25 Sep 2010 12:42:55 +0200 Subject: 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 (Moved the checks above the position checks /Jens) Signed-off-by: Jens Axboe --- block/blk-merge.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'block/blk-merge.c') 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 @@ static int attempt_merge(struct request_queue *q, struct request *req, 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)) -- cgit v1.1