linux-kernel - Re: [syzbot] unexpected kernel reboot (4)

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Message-ID: <d829f5a8-95ba-1a17-c36a-21e23d382875@i-love.sakura.ne.jp>
Date:   Fri, 23 Apr 2021 01:13:03 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        syzbot <syzbot+9ce030d4c89856b27619@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [syzbot] unexpected kernel reboot (4)

On 2021/04/22 23:20, Dmitry Vyukov wrote:
> I've prepared this syzkaller change:
> https://github.com/google/syzkaller/pull/2550/files

OK. Please merge and let's see whether syzkaller can find different ways.

In my environment, this problem behaves very puzzling. While the reproducer
I use is single threaded, changing timing via CONFIG_DEBUG_KOBJECT=y or
even https://syzkaller.appspot.com/x/patch.diff?x=13d69ffed00000 avoids
this problem. I can't narrow down what is happening.

> 
> Re hibernation/suspend configs, you said disabling them is not
> helping, right? Does it still make sense to disable them?
> If these configs are enabled, we can at least find some bugs in the
> preparation for suspend code. However, as you noted, it will
> immediately lead to "lost connection".
> Ideally we somehow tweak hibernation/suspend to get to the
> hibernation/suspend point and then immediately and automatically
> resume.

That will be one of disable-specific-functionality changes.

>         This way we could test both suspend and unsuspend code, which
> I assume can lead to bugs, and don't cause "lost connection" at the
> same time. I guess such a mode does not exist today... and I am not
> sure what happens with TCP connections after this.

I don't know whether ssh sessions can survive 10 seconds of
hibernation/suspend. But maybe disabling hibernation/suspend configs
until disable-specific-functionality changes are accepted makes sense.