Subject: Re: bio linked list corruption.
To: Chris Mason <clm@fb.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Jones <davej@codemonkey.org.uk>,
        Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
        "Josef Bacik" <jbacik@fb.com>, David Sterba <dsterba@suse.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Dave Chinner <david@fromorbit.com>
References: <CA+55aFzsrRenu3NsDYr3qqO=fC9FUxkLc3M2wzeLBpN7ghwvwA@mail.gmail.com>
 <20161026184201.6ofblkd3j5uxystq@codemonkey.org.uk>
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 <2bdc068d-afd5-7a78-f334-26970c91aaca@fb.com>
 <20161026231950.GB15247@clm-mbp.thefacebook.com>
From: Jens Axboe <axboe@fb.com>
Message-ID: <2951bc27-2453-203a-009d-260bccf2d038@fb.com>
Date: Wed, 26 Oct 2016 17:21:22 -0600
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On 10/26/2016 05:19 PM, Chris Mason wrote:
> On Wed, Oct 26, 2016 at 05:03:45PM -0600, Jens Axboe wrote:
>> On 10/26/2016 04:58 PM, Linus Torvalds wrote:
>>> On Wed, Oct 26, 2016 at 3:51 PM, Linus Torvalds
>>> <torvalds@linux-foundation.org> wrote:
>>>>
>>>> Dave: it might be a good idea to split that "WARN_ON_ONCE()" in
>>>> blk_mq_merge_queue_io() into two
>>>
>>> I did that myself too, since Dave sees this during boot.
>>>
>>> But I'm not getting the warning ;(
>>>
>>> Dave gets it with ext4, and thats' what I have too, so I'm not sure
>>> what the required trigger would be.
>>
>> Actually, I think I see what might trigger it. You are on nvme, iirc,
>> and that has a deep queue. Dave, are you testing on a sata drive or
>> something similar with a shallower queue depth? If we end up sleeping
>> for a request, I think we could trigger data->ctx being different.
>>
>> Dave, can you hit the warnings with this? Totally untested...
>
> Confirmed, totally untested ;)  Don't try this one at home folks
> (working this out with Jens offlist)

Ahem, I did say untested! The one I just sent in reply to Linus should
be better. Though that one is completely untested as well...

-- 
Jens Axboe