On Fri, Oct 19, 2018 at 11:52:36AM -0400, valdis.kletnieks@xxxxxx wrote: > On Wed, 17 Oct 2018 17:20:29 -0400, Dennis Zhou said: > > > > I apologize, but I'm having a hard time reproducing this myself. I am > > not able to hit this issue in my qemu instance with linux-next built > > with your config. I have been running 'rpm -Hvh --force fio.rpm' several > > times and haven't seen the issue. > > I wouldn't be surprised if there's something oddball in my system config > that changes the situation. > Do you by chance run any encryption or anything on top of your hard drive or ssd? > > Would it be possible for you to create a minimal qemu image that > > reproduces the issue as I'm having issues reproducing it with my setup? > > Hmm.. I'd first have to figure out how to build a qemu image at all.. > > > Additionally, I've added some more debug text in the diff below. If you > > could apply that and send me the full dmesg that would be great. Lastly, > > can you just confirm for me that the commit before, f0fcb3ec89f3 > > "blkcg: remove additional reference to the css", isn't seeing this > > issue? > > Full dmesg attached. Had to piece it together from a 'dmesg' and what > got saved in pstore when it crashed. I was surprised that the printk_once > popped during very early boot (2.88 seconds in), and then only 2 lines of output > right before the crash: > > [ 106.465848] audit: type=1130 audit(1539957798.984:101): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:syst > em_r:init_t:s0-s15:c0.c1023 msg='unit=run-r93ac4731e4724fd6a3670e7d0c417522 comm="systemd" exe="/usr/lib/systemd/systemd > " hostname=? addr=? terminal=? res=success' > [ 106.564711] dennis: q ffff9e3c57152000 != rl->q ffff9e3a8fe48040 > [ 106.564713] dennis: bio: ffff9e3a8fcf5400, root: ffffffffbbdd89e0 > [ 106.564761] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 > [ 106.568786] PGD 0 P4D 0 > [ 106.570761] Oops: 0000 [#1] PREEMPT SMP PTI > [ 106.573115] CPU: 2 PID: 1205 Comm: sh Tainted: G T 4.19.0-rc8-next-20181016-dirty #639 > > I'll cook up a kernel checked out at that commit and test later today... I thought of another issue that may explain what's going on. It has to do with how a bio can go through make_request() several times. However, I do association on the first entry, but subsequent requests may go to separate queues. Therefore association and the blk_get_rl() returns the wrong request_list. It may be that a particular blkg doesn't have a fully initialized request_list. I've currently only been testing on a drive directly, but my try with md still worked.. So I am still trying other ways to reproduce it. Thanks for being patient with me. Would you be able to try the following on Jens' for-4.20/block branch? His tree is available here: https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git Thanks, Dennis --- block/bio.c | 20 ++++++++++++++++++++ block/blk-core.c | 1 + include/linux/bio.h | 3 +++ 3 files changed, 24 insertions(+) diff --git a/block/bio.c b/block/bio.c index 17a8b0aa7050..bbfeb4ee2892 100644 --- a/block/bio.c +++ b/block/bio.c @@ -2083,6 +2083,26 @@ int bio_associate_create_blkg(struct request_queue *q, struct bio *bio) return ret; } +/** + * bio_reassociate_blkg - reassociate a bio with a blkg from q + * @q: request_queue where bio is going + * @bio: target bio + * + * When submitting a bio, multiple recursive calls to make_request() may occur. + * This causes the initial associate done in blkcg_bio_issue_check() to be + * incorrect and reference the prior request_queue. This performs reassociation + * when this situation happens. + */ +int bio_reassociate_blkg(struct request_queue *q, struct bio *bio) +{ + if (bio->bi_blkg) { + blkg_put(bio->bi_blkg); + bio->bi_blkg = NULL; + } + + return bio_associate_create_blkg(q, bio); +} + /** * bio_disassociate_task - undo bio_associate_current() * @bio: target bio diff --git a/block/blk-core.c b/block/blk-core.c index cdfabc5646da..3ed60723e242 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -2433,6 +2433,7 @@ blk_qc_t generic_make_request(struct bio *bio) if (q) blk_queue_exit(q); q = bio->bi_disk->queue; + bio_reassociate_blkg(q, bio); flags = 0; if (bio->bi_opf & REQ_NOWAIT) flags = BLK_MQ_REQ_NOWAIT; diff --git a/include/linux/bio.h b/include/linux/bio.h index f447b0ebb288..b47c7f716731 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -514,6 +514,7 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg); int bio_associate_blkg_from_css(struct bio *bio, struct cgroup_subsys_state *css); int bio_associate_create_blkg(struct request_queue *q, struct bio *bio); +int bio_reassociate_blkg(struct request_queue *q, struct bio *bio); void bio_disassociate_task(struct bio *bio); void bio_clone_blkg_association(struct bio *dst, struct bio *src); #else /* CONFIG_BLK_CGROUP */ @@ -522,6 +523,8 @@ static inline int bio_associate_blkg_from_css(struct bio *bio, { return 0; } static inline int bio_associate_create_blkg(struct request_queue *q, struct bio *bio) { return 0; } +static inline int bio_reassociate_blkg(struct request_queue *q, struct bio *bio) +{ return 0; } static inline void bio_disassociate_task(struct bio *bio) { } static inline void bio_clone_blkg_association(struct bio *dst, struct bio *src) { } -- 2.17.1
