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 --- include/linux/blk_types.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/blk_types.h') diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 46c005d601ac..fc99474ac968 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -228,6 +228,7 @@ struct bio { #define BIO_TRACE_COMPLETION 10 /* bio_endio() should trace the final completion * of this bio. */ #define BIO_QUEUE_ENTERED 11 /* can use blk_queue_enter_live() */ +#define BIO_TRACKED 12 /* set if bio goes through the rq_qos path */ /* See BVEC_POOL_OFFSET below before adding new flags */ -- cgit