On Wed, Jun 05, 2019 at 02:42:27PM +0200, gregkh wrote:
> On Wed, Jun 05, 2019 at 08:21:44PM +0800, Alvin Zheng wrote:
> > Hi,
> > I was using kernel v4.19.48 and found that it cannot pass the generic/538 on xfs. The error output is as follows:
>
> Has 4.19 ever been able to pass that test? If not, I wouldn't worry
> about it :)
>
FWIW, the fstests commit references the following kernel patches for
fixes in XFS and ext4:
xfs: serialize unaligned dio writes against all other dio writes
ext4: fix data corruption caused by unaligned direct AIO
It looks like both of those patches landed in 5.1.
Brian
> >
> > FSTYP -- xfs (non-debug)
> > PLATFORM -- Linux/x86_64 alinux2-6 4.19.48
> > MKFS_OPTIONS -- -f -bsize=4096 /dev/vdc
> > MOUNT_OPTIONS -- /dev/vdc /mnt/testarea/scra
> > generic/538 0s ... - output mismatch (see /root/usr/local/src/xfstests/results//generic/538.out.bad)
> > --- tests/generic/538.out 2019-05-27 13:57:06.505666465 +0800
> > +++ /root/usr/local/src/xfstests/results//generic/538.out.bad 2019-06-05 16:43:14.702002326 +0800
> > @@ -1,2 +1,10 @@
> > QA output created by 538
> > +Data verification fails
> > +Find corruption
> > +00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> > +*
> > +00000200 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
> > +00002000
> > ...
> > (Run 'diff -u /root/usr/local/src/xfstests/tests/generic/538.out /root/usr/local/src/xfstests/results//generic/538.out.bad' to see the entire diff)
> > Ran: generic/538
> > Failures: generic/538
> > Failed 1 of 1 tests
> >
> > I also found that the latest kernel (v5.2.0-rc2) of upstream can pass the generic/538 test. Therefore, I bisected and found the first good commit is 3110fc79606. This commit adds the hardware queue into the sort function. Besides, the sort function returns a negative value when the offset and queue (software and hardware) of two I/O requests are same. I think the second part of the change make senses. The kernel should not change the relative position of two I/O requests when their offset and queue are same. So I made the following changes and merged it into the kernel 4.19.48. After the modification, we can pass the generic/538 test on xfs. The same case can be passed on ext4, since ext4 has corresponding fix 0db24122bd7f ("ext4: fix data corruption caused by overlapping unaligned and aligned IO"). Though I think xfs should be responsible for this issue, the block layer code below is also problematic. Any ideas?
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 4e563ee..a7309cd 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -1610,7 +1610,7 @@ static int plug_ctx_cmp(void *priv, struct list_head *a, struct list_head *b)
> >
> > return !(rqa->mq_ctx < rqb->mq_ctx ||
> > (rqa->mq_ctx == rqb->mq_ctx &&
> > - blk_rq_pos(rqa) < blk_rq_pos(rqb)));
> > + blk_rq_pos(rqa) <= blk_rq_pos(rqb)));
> > }
> >
> > void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
>
> I would not like to take a patch that is not upstream, but rather take
> the original commit.
>
> Can 3110fc79606f ("blk-mq: improve plug list sorting") on its own
> resolve this issue for 4.19.y?
>
> thanks,
>
> greg k-h
