linux-kernel - Re: INFO: task hung in __blkdev

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Date:   Tue, 10 Apr 2018 15:24:46 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Jens Axboe <axboe@...nel.dk>, Ming Lei <tom.leiming@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        syzbot 
        <bot+48594378e9851eab70bcd6f99327c7db58c5a28a@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Omar Sandoval <osandov@...com>
Subject: Re: INFO: task hung in __blkdev_get

On Tue, Apr 10, 2018 at 3:04 PM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> Dmitry Vyukov wrote:
>> On Tue, Apr 10, 2018 at 12:55 PM, Tetsuo Handa
>> <penguin-kernel@...ove.sakura.ne.jp> wrote:
>> > Hello.
>> >
>> > Since syzbot is reporting so many hung up bug which involves /dev/loopX ,
>> > is it possible to "temporarily" apply below patch for testing under syzbot
>>
>> Unfortunately it's not possible, for full explanation please see:
>> https://github.com/google/syzkaller/blob/master/docs/syzbot.md#no-custom-patches
>>
>
> I mean, sending custom patch to linux.git for -rc and revert the custom patch
> before -final is released. It won't take so much period until we get the result.

Ah, I see, then I guess it wasn't a question to me.

> If syzbot can test arbitrary git tree instead of linux.git, making a branch
> which contains custom patches would be possible.

syzbot tests a set of trees (also net-next and bpf-next at the
moment). But see this reply to Takashi re a similar request:
https://groups.google.com/forum/#!msg/syzkaller-bugs/7ucgCkAJKSk/skZjgavRAQAJ
Note that a syzkaller instances will produce several hundreds of
different crashes within a day, and then a big question is what to do
with them.

What's perfectly possible though is running syzkaller locally, and you
can do it on just any tree you want. I've recently put a script that
setups syzkaller end-to-end with config, compiler and image that
syzbot uses:
https://github.com/google/syzkaller/blob/master/tools/demo_setup.sh
(that uses v4.13, but you can change this to any kernel version).