From: Dennis Zhou dennis@kernel.org

mainline inclusion from mainline-v5.0-rc1 commit 13369816cb648f897ce9cbf57e55eeb742ce4eb3 category: bugfix bugzilla: 182234 CVE: NA ---------------------------

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 dennis@kernel.org Cc: Josef Bacik josef@toxicpanda.com Signed-off-by: Jens Axboe axboe@kernel.dk

Conflicts: block/blk-iolatency.c block/blk-rq-qos.c Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- block/blk-iolatency.c | 2 +- block/blk-rq-qos.c | 6 ++++++ include/linux/blk_types.h | 1 + 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index 8897f7c579ec7..b10336b401f6e 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -563,7 +563,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) int inflight = 0;

blkg = bio->bi_blkg; - if (!blkg) + if (!blkg || !bio_flagged(bio, BIO_TRACKED)) return;

iolat = blkg_to_lat(bio->bi_blkg); diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index 8f277518b21ba..86456d016cf92 100644 --- a/block/blk-rq-qos.c +++ b/block/blk-rq-qos.c @@ -72,6 +72,12 @@ void rq_qos_throttle(struct request_queue *q, struct bio *bio, { struct rq_qos *rqos;

+ /* + * BIO_TRACKED lets controllers know that a bio went through the + * normal rq_qos path. + */ + bio_set_flag(bio, BIO_TRACKED); + for(rqos = q->rq_qos; rqos; rqos = rqos->next) { if (rqos->ops->throttle) rqos->ops->throttle(rqos, bio, lock); diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 29ffec0814e9a..78e701f34dc42 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -236,6 +236,7 @@ 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 */