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 10:18:48 +0100
From:   Andre Tomt <andre@...t.net>
To:     Jack Wang <jack.wang.usish@...il.com>
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)

On 16.12.2019 08:42, Jack Wang wrote:
> Andre Tomt <andre@...t.net> 于2019年12月14日周六 下午3:24写道：
>>
>> 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"

Indeed, adding this commit on top a clean 4.19.89 fixes the issue. So 
far survived about an hour of rsyncing file churn.