| Message ID | 20151123232134.4abda9a7@tom-T450 (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Delegated to: | Jens Axboe |
| Headers | show |
On 11/23/2015 10:21 AM, Ming Lei wrote: > On Mon, 23 Nov 2015 10:46:20 +0800 > Ming Lei <ming.lei@canonical.com> wrote: > >> Hi Mark, >> >> On Mon, Nov 23, 2015 at 9:50 AM, Mark Salter <msalter@redhat.com> wrote: >>> On Mon, 2015-11-23 at 08:36 +0800, Ming Lei wrote: >>>> On Mon, Nov 23, 2015 at 7:20 AM, Mark Salter <msalter@redhat.com> wrote: >>>>> On Sun, 2015-11-22 at 00:56 +0800, Ming Lei wrote: >>>>>> On Sat, 21 Nov 2015 12:30:14 +0100 >>>>>> Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote: >>>>>> >>>>>>> On 20/11/2015 13:10, Michael Ellerman wrote: >>>>>>>> On Thu, 2015-11-19 at 00:23 -0800, Christoph Hellwig wrote: >>>>>>>> >>>>>>>>> It's pretty much guaranteed a block layer bug, most likely in the >>>>>>>>> merge bios to request infrastucture where we don't obey the merging >>>>>>>>> limits properly. >>>>>>>>> >>>>>>>>> Does either of you have a known good and first known bad kernel? >>>>>>>> >>>>>>>> Not me, I've only hit it one or two times. All I can say is I have hit it in >>>>>>>> 4.4-rc1. >>>>>>>> >>>>>>>> Laurent, can you narrow it down at all? >>>>>>> >>>>>>> It seems that the panic is triggered by the commit bdced438acd8 ("block: >>>>>>> setup bi_phys_segments after splitting") which has been pulled by the >>>>>>> merge d9734e0d1ccf ("Merge branch 'for-4.4/core' of >>>>>>> git://git.kernel.dk/linux-block"). >>>>>>> >>>>>>> My system is panicing promptly when running a kernel built at >>>>>>> d9734e0d1ccf, while reverting the commit bdced438acd8, it can run hours >>>>>>> without panicing. >>>>>>> >>>>>>> This being said, I can't explain what's going wrong. >>>>>>> >>>>>>> May Ming shed some light here ? >>>>>> >>>>>> Laurent, looks there is one bug in blk_bio_segment_split(), would you >>>>>> mind testing the following patch to see if it fixes your issue? >>>>>> >>>>>> --- >>>>>> From 6fc701231dcc000bc8bc4b9105583380d9aa31f4 Mon Sep 17 00:00:00 2001 >>>>>> From: Ming Lei <ming.lei@canonical.com> >>>>>> Date: Sun, 22 Nov 2015 00:47:13 +0800 >>>>>> Subject: [PATCH] block: fix segment split >>>>>> >>>>>> Inside blk_bio_segment_split(), previous bvec pointer('bvprvp') >>>>>> always points to the iterator local variable, which is obviously >>>>>> wrong, so fix it by pointing to the local variable of 'bvprv'. >>>>>> >>>>>> Signed-off-by: Ming Lei <ming.lei@canonical.com> >>>>>> --- >>>>>> block/blk-merge.c | 4 ++-- >>>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/block/blk-merge.c b/block/blk-merge.c >>>>>> index de5716d8..f2efe8a 100644 >>>>>> --- a/block/blk-merge.c >>>>>> +++ b/block/blk-merge.c >>>>>> @@ -98,7 +98,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, >>>>>> >>>>>> seg_size += bv.bv_len; >>>>>> bvprv = bv; >>>>>> - bvprvp = &bv; >>>>>> + bvprvp = &bvprv; >>>>>> sectors += bv.bv_len >> 9; >>>>>> continue; >>>>>> } >>>>>> @@ -108,7 +108,7 @@ new_segment: >>>>>> >>>>>> nsegs++; >>>>>> bvprv = bv; >>>>>> - bvprvp = &bv; >>>>>> + bvprvp = &bvprv; >>>>>> seg_size = bv.bv_len; >>>>>> sectors += bv.bv_len >> 9; >>>>>> } >>>>> >>>>> I'm still hitting the BUG even with this patch applied on top of 4.4-rc1. >>>> >>>> OK, looks there are still other bugs, care to share us how to reproduce >>>> it on arm64? >>>> >>>> thanks, >>>> Ming >>> >>> Unfortunately, the best reproducer I have is to boot the platform. I have seen the >>> BUG a few times post-boot, but I don't have a consistant reproducer. I am using >>> upstream 4.4-rc1 with this config: >>> >>> http://people.redhat.com/msalter/fh_defconfig >>> >>> With 4.4-rc1 on an APM Mustang platform, I see the BUG about once every 6-7 boots. >>> On an AMD Seattle platform, about every 9 boots. >> >> Thanks for the input, and I will try to reproduce the issue on mustang with >> your kernel config. > > I can reproduce the issue on mustang, and looks I may understand the story now. > > When 64K page size is used on arm64, and the default segment size of block > is 65536, then one segment should only include one page at most. > > Commit bdced438acd83a(block: setup bi_phys_segments after splitting) does not > compute bio->bi_seg_front_size and bio->bi_seg_back_size, then one less segment > may be obtained because blk_phys_contig_segment() thought the last bvec in 1st > bio and the 1st bvec in the 2nd bio is in one physical segment, so cause the > regression. > > Looks the following patch can fix the issue by figuring bio->bi_seg_front_size > and bio->bi_seg_back_size in blk_bio_segment_split(). > > Mark, thanks again for providing the reproduction steps, and could you run your > test to see if it can fix your issue? > > --- > From 86b5f33d48715c1150fdcfd9a76e495e7aa913aa Mon Sep 17 00:00:00 2001 > From: Ming Lei <ming.lei@canonical.com> > Date: Mon, 23 Nov 2015 20:27:23 +0800 > Subject: [PATCH 2/2] blk-merge: fix blk_bio_segment_split > > Commit bdced438acd83a(block: setup bi_phys_segments after > splitting) introduces function of computing bio->bi_phys_segments > during bio splitting. > > Unfortunately both bio->bi_seg_front_size and bio->bi_seg_back_size > arn't computed, so too many physical segments may be obtained > for one request since both the two are used to check if one segment > across two bios can be possible. > > This patch fixes the issue by computing the two variables in > blk_bio_segment_split(). > > Reported-by: Michael Ellerman <mpe@ellerman.id.au> > Reported-by: Mark Salter <msalter@redhat.com> > Fixes: bdced438acd83a(block: setup bi_phys_segments after splitting) > Signed-off-by: Ming Lei <ming.lei@canonical.com> > --- > block/blk-merge.c | 22 +++++++++++++++++++--- > 1 file changed, 19 insertions(+), 3 deletions(-) > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index f2efe8a..50793cd 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -76,6 +76,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, > struct bio_vec bv, bvprv, *bvprvp = NULL; > struct bvec_iter iter; > unsigned seg_size = 0, nsegs = 0, sectors = 0; > + unsigned front_seg_size = bio->bi_seg_front_size; > + bool do_split = true; > + struct bio *new = NULL; > > bio_for_each_segment(bv, bio, iter) { > if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q)) > @@ -111,13 +114,26 @@ new_segment: > bvprvp = &bvprv; > seg_size = bv.bv_len; > sectors += bv.bv_len >> 9; > + > + if (nsegs == 1 && seg_size > front_seg_size) > + front_seg_size = seg_size; > } > > - *segs = nsegs; > - return NULL; > + do_split = false; > split: > *segs = nsegs; > - return bio_split(bio, sectors, GFP_NOIO, bs); > + > + if (do_split) { > + new = bio_split(bio, sectors, GFP_NOIO, bs); > + if (new) > + bio = new; > + } > + > + bio->bi_seg_front_size = front_seg_size; > + if (seg_size > bio->bi_seg_back_size) > + bio->bi_seg_back_size = seg_size; > + > + return do_split ? new : NULL; > } > > void blk_queue_split(struct request_queue *q, struct bio **bio, > I applied both your patches and tested on Overdrive 3000. This fixes the issue for me. Added linux-arm-kernel, since arm64 triggers this issue. Thanks Ming and testers for your hard work on this. Tested-by: Alan Ott <alan@softiron.co.uk> -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/block/blk-merge.c b/block/blk-merge.c index f2efe8a..50793cd 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -76,6 +76,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, struct bio_vec bv, bvprv, *bvprvp = NULL; struct bvec_iter iter; unsigned seg_size = 0, nsegs = 0, sectors = 0; + unsigned front_seg_size = bio->bi_seg_front_size; + bool do_split = true; + struct bio *new = NULL; bio_for_each_segment(bv, bio, iter) { if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q)) @@ -111,13 +114,26 @@ new_segment: bvprvp = &bvprv; seg_size = bv.bv_len; sectors += bv.bv_len >> 9; + + if (nsegs == 1 && seg_size > front_seg_size) + front_seg_size = seg_size; } - *segs = nsegs; - return NULL; + do_split = false; split: *segs = nsegs; - return bio_split(bio, sectors, GFP_NOIO, bs); + + if (do_split) { + new = bio_split(bio, sectors, GFP_NOIO, bs); + if (new) + bio = new; + } + + bio->bi_seg_front_size = front_seg_size; + if (seg_size > bio->bi_seg_back_size) + bio->bi_seg_back_size = seg_size; + + return do_split ? new : NULL; } void blk_queue_split(struct request_queue *q, struct bio **bio,