linux-kernel - Re: [PATCH 4.19 153/306] block: fix the DISCARD request merge (4.19.87+ crash)

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Date:   Mon, 16 Dec 2019 08:42:05 +0100
From:   Jack Wang <jack.wang.usish@...il.com>
To:     Andre Tomt <andre@...t.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>,
        Christoph Hellwig <hch@....de>, Ming Lei <ming.lei@...hat.com>,
        Jianchao Wang <jianchao.w.wang@...cle.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 153/306] block: fix the DISCARD request merge
 (4.19.87+ crash)

Andre Tomt <andre@...t.net> 于2019年12月14日周六 下午3:24写道：
>
> On 27.11.2019 21:30, Greg Kroah-Hartman wrote:
> > From: Jianchao Wang <jianchao.w.wang@...cle.com>
> >
> > [ Upstream commit 69840466086d2248898020a08dda52732686c4e6 ]
> >
> > There are two cases when handle DISCARD merge.
> > If max_discard_segments == 1, the bios/requests need to be contiguous
> > to merge. If max_discard_segments > 1, it takes every bio as a range
> > and different range needn't to be contiguous.
> >
> > But now, attempt_merge screws this up. It always consider contiguity
> > for DISCARD for the case max_discard_segments > 1 and cannot merge
> > contiguous DISCARD for the case max_discard_segments == 1, because
> > rq_attempt_discard_merge always returns false in this case.
> > This patch fixes both of the two cases above.
> >
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > Reviewed-by: Ming Lei <ming.lei@...hat.com>
> > Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
> > Signed-off-by: Jens Axboe <axboe@...nel.dk>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
>
> 4.19.87, 4.19.88, 4.19.89 all lock up frequently on some of my systems.
> The same systems run 5.4.3 fine, so the newer trees are probably OK.
> Reverting this commit on top of 4.19.87 makes everything stable.
>
> To trigger it all I have to do is re-rsyncing a directory tree with some
> changed files churn, it will usually crash in 10 to 30 minutes.
>
> The systems crashing has ext4 filesystem on a two ssd md raid1 mounted
> with the mount option discard. If mounting it without discard, the
> crashes no longer seem to occur.
>
> No oops/panic made it to the ipmi console. I suspect the console is just
> misbehaving and it didnt really livelock. At one point one line of the
> crash made it to the console (kernel BUG at block/blk-core.c:1776), and
> it was enough to pinpoint this commit. Note that the line number might
> be off, as I was attempting a bisect at the time.
>
> This commit also made it to 4.14.x, but I have not tested it.
Hi Andre,

I noticed one fix is missing for discard merge in 4.19.y
2a5cf35cd6c5 ("block: fix single range discard merge")

Can you try if it helps? just "git cherry-pick 2a5cf35cd6c5"

Thanks
Jack Wang