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authorJan Kara <jack@suse.cz>2020-06-05 16:16:16 +0200
committerJens Axboe <axboe@kernel.dk>2021-01-27 17:15:38 +0100
commit41e76c85660c022c6bf5713bfb6c21e64a487cec (patch)
tree470e919856dcf53ea851f883e705983580b7b131 /block/bfq-iosched.c
parentblkcg: delete redundant get/put operations for queue (diff)
downloadlinux-41e76c85660c022c6bf5713bfb6c21e64a487cec.tar.xz
linux-41e76c85660c022c6bf5713bfb6c21e64a487cec.zip
bfq: Avoid false bfq queue merging
bfq_setup_cooperator() uses bfqd->in_serv_last_pos so detect whether it makes sense to merge current bfq queue with the in-service queue. However if the in-service queue is freshly scheduled and didn't dispatch any requests yet, bfqd->in_serv_last_pos is stale and contains value from the previously scheduled bfq queue which can thus result in a bogus decision that the two queues should be merged. This bug can be observed for example with the following fio jobfile: [global] direct=0 ioengine=sync invalidate=1 size=1g rw=read [reader] numjobs=4 directory=/mnt where the 4 processes will end up in the one shared bfq queue although they do IO to physically very distant files (for some reason I was able to observe this only with slice_idle=1ms setting). Fix the problem by invalidating bfqd->in_serv_last_pos when switching in-service queue. Fixes: 058fdecc6de7 ("block, bfq: fix in-service-queue check for queue merging") CC: stable@vger.kernel.org Signed-off-by: Jan Kara <jack@suse.cz> Acked-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/bfq-iosched.c')
-rw-r--r--block/bfq-iosched.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 23e293d2943c..4157cfe99ae2 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -3007,6 +3007,7 @@ static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
}
bfqd->in_service_queue = bfqq;
+ bfqd->in_serv_last_pos = 0;
}
/*