On Fri, 11 Sep 2015 17:43:15 -0400 Mike Snitzer <snit...@redhat.com> wrote:
> Ming, Jens, others: > > Please see this BZ comment that speaks to a 4.3 regression due to the > late bio splitting changes: > https://bugzilla.redhat.com/show_bug.cgi?id=1247382#c41 I think it is a bug of bounce_end_io, and the following patch may fix it. ---- >From 08df0db0be41e6bea306bcf5b4d325f5a79dc7a1 Mon Sep 17 00:00:00 2001 From: Ming Lei <ming....@canonical.com> Date: Sat, 12 Sep 2015 20:48:42 +0800 Subject: [PATCH] block: fix bounce_end_io When bio bounce is involved, one new bio and its io vector are cloned from the coming bio, which can be one fast-cloned bio and its io vector can be shared with another bio too, especially after bio_split() is introduced. So it is obviously wrong to assume the start index of the original bio's io vector is zero, which can be any value between 0 and (bi_max_vecs - 1), especially in case of bio split. Signed-off-by: Ming Lei <ming....@canonical.com> --- block/bounce.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/block/bounce.c b/block/bounce.c index 0611aea..1cb5dd3 100644 --- a/block/bounce.c +++ b/block/bounce.c @@ -128,12 +128,14 @@ static void bounce_end_io(struct bio *bio, mempool_t *pool) struct bio *bio_orig = bio->bi_private; struct bio_vec *bvec, *org_vec; int i; + int start = bio_orig->bi_iter.bi_idx; /* * free up bounce indirect pages used */ bio_for_each_segment_all(bvec, bio, i) { - org_vec = bio_orig->bi_io_vec + i; + org_vec = bio_orig->bi_io_vec + i + start; + if (bvec->bv_page == org_vec->bv_page) continue; -- 1.9.1 > But inlined here so we can continue on list: > (In reply to Josh Boyer from comment #40) > > The function that was fixed in 4.2 doesn't exist any longer in > > 4.3.0-0.rc0.git6.1.fc24. That kernel corresponds to Linux > > v4.2-6105-gdd5cdb48edfd which contains commit > > 8ae126660fddbeebb9251a174e6fa45b6ad8f932, which removed it completely. So > > whatever fix was made in dm_merge_bvec doesn't seem to have made it to > > whatever replaced it. > > The dm core fix to dm_merge_bvec was commit bd4aaf8f9b ("dm: fix > dm_merge_bvec regression on 32 bit systems"). But I'm not sure there is > a clear equivalent in the late bio splitting code that replaced block > core's merge_bvec logic. > > merge_bvec was all about limiting bios (by asking "can/should this page > be added to this bio?") whereas the late bio splitting is more "build > the bios as large as possible and worry about splitting later". IMO, given one vector can only point to one page, there shouldn't have difference between the two. > > Regardless, this regression needs to be reported to Ming Lin > <min...@ssi.samsung.com>, Jens Axboe and the others involved in > maintaining the late bio splitting changes in block core. > > Josh and/or Adam: it would _really_ help if the regression test you guys > are using could be handed-over and/or explained to us. Is it as simple > as loading a 32bit with a particular config? Can you share the guest > image if it is small enough? Josh, Adam, would you mind testing the above patch to see if it can fix your issue? Thanks, Ming > > Mike > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
