From 13369816cb648f897ce9cbf57e55eeb742ce4eb3 Mon Sep 17 00:00:00 2001 From: Dennis Zhou Date: Mon, 17 Dec 2018 11:03:51 -0500 Subject: block: fix blk-iolatency accounting underflow The blk-iolatency controller measures the time from rq_qos_throttle() to rq_qos_done_bio() and attributes this time to the first bio that needs to create the request. This means if a bio is plug-mergeable or bio-mergeable, it gets to bypass the blk-iolatency controller. The recent series [1], to tag all bios w/ blkgs undermined how iolatency was determining which bios it was charging and should process in rq_qos_done_bio(). Because all bios are being tagged, this caused the atomic_t for the struct rq_wait inflight count to underflow and result in a stall. This patch adds a new flag BIO_TRACKED to let controllers know that a bio is going through the rq_qos path. blk-iolatency now checks if this flag is set to see if it should process the bio in rq_qos_done_bio(). Overloading BLK_QUEUE_ENTERED works, but makes the flag rules confusing. BIO_THROTTLED was another candidate, but the flag is set for all bios that have gone through blk-throttle code. Overloading a flag comes with the burden of making sure that when either implementation changes, a change in setting rules for one doesn't cause a bug in the other. So here, we unfortunately opt for adding a new flag. [1] https://lore.kernel.org/lkml/20181205171039.73066-1-dennis@kernel.org/ Fixes: 5cdf2e3fea5e ("blkcg: associate blkg when associating a device") Signed-off-by: Dennis Zhou Cc: Josef Bacik Signed-off-by: Jens Axboe --- block/blk-rq-qos.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'block/blk-rq-qos.h') diff --git a/block/blk-rq-qos.h b/block/blk-rq-qos.h index 3c85f26d3846..564851889550 100644 --- a/block/blk-rq-qos.h +++ b/block/blk-rq-qos.h @@ -168,6 +168,11 @@ static inline void rq_qos_done_bio(struct request_queue *q, struct bio *bio) static inline void rq_qos_throttle(struct request_queue *q, struct bio *bio) { + /* + * BIO_TRACKED lets controllers know that a bio went through the + * normal rq_qos path. + */ + bio_set_flag(bio, BIO_TRACKED); if (q->rq_qos) __rq_qos_throttle(q->rq_qos, bio); } -- cgit v1.2.3