From ab0fd1debe730ec9998678a0c53caefbd121ed10 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 3 Jul 2009 12:56:18 +0200 Subject: [PATCH] block: don't merge requests of different failfast settings References: bnc#519111 Block layer used to merge requests and bios with different failfast settings. This caused regular IOs to fail prematurely when they were merged into failfast requests for readahead. Niel Lambrechts could trigger the problem semi-reliably on ext4 when resuming from STR. ext4 uses readahead when reading inodes and combined with the deterministic extra SATA PHY exception cycle during resume on the specific configuration, non-readahead inode read would fail causing ext4 errors. Please read the following thread for details. http://lkml.org/lkml/2009/5/23/21 This patch makes block layer reject merging if the failfast settings don't match. This is correct but likely to lower IO performance by preventing regular IOs from mingling into surrounding readahead requests. Changes to allow such mixed merges and handle errors correctly will be added later. Signed-off-by: Tejun Heo Reported-by: Niel Lambrechts Cc: Theodore Tso Signed-off-by: Jens Axboe Signed-off-by: Tejun Heo --- block/blk-merge.c | 6 ++++++ block/elevator.c | 8 ++++++++ 2 files changed, 14 insertions(+) --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -376,6 +376,12 @@ static int attempt_merge(struct request_ if (blk_integrity_rq(req) != blk_integrity_rq(next)) return 0; + /* don't merge requests of different failfast settings */ + if (blk_failfast_dev(req) != blk_failfast_dev(next) || + blk_failfast_transport(req) != blk_failfast_transport(next) || + blk_failfast_driver(req) != blk_failfast_driver(next)) + return 0; + /* * If we are allowed to merge, then append bio list * from next to rq and release next. merge_requests_fn --- a/block/elevator.c +++ b/block/elevator.c @@ -97,6 +97,14 @@ int elv_rq_merge_ok(struct request *rq, if (bio_integrity(bio) != blk_integrity_rq(rq)) return 0; + /* + * Don't merge if failfast settings don't match + */ + if (!bio_failfast_dev(bio) != !blk_failfast_dev(rq) || + !bio_failfast_transport(bio) != !blk_failfast_transport(rq) || + !bio_failfast_driver(bio) != !blk_failfast_driver(rq)) + return 0; + if (!elv_iosched_allow_merge(rq, bio)) return 0;