The xfs patch (xfs: serialize unaligned dio writes against all other dio writes) does fix the data corruption bug of kernel 4.19 on xfs.
As for 3110fc79606f ("blk-mq: improve plug list sorting"), it happens to fix the logic error of the sort function in the block layer and it is based on the multiple maps of the blk-mq which was introduced in v5.0. Therefore, backporting this commit will introduce a lot of relevant code.
Regards,
Alvin
------------------------------------------------------------------
From:gregkh <gregkh@xxxxxxxxxxxxxxxxxxx>
Send Time:2019年6月5日(星期三) 20:42
To:Alvin Zheng <Alvin@xxxxxxxxxxxxxxxxx>
Cc:darrick.wong <darrick.wong@xxxxxxxxxx>; axboe <axboe@xxxxxxxxx>; linux-block <linux-block@xxxxxxxxxxxxxxx>; linux-xfs <linux-xfs@xxxxxxxxxxxxxxx>; caspar <caspar@xxxxxxxxxxxxxxxxx>; joseph.qi <joseph.qi@xxxxxxxxxxxxxxxxx>
Subject:Re: [bug report][stable] xfstests:generic/538 failed on xfs
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 :)
>
> 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
