linux-kernel - Re: watchdog: BUG: soft lockup

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Message-ID: <CAGXGE_JaVxfpsGh4qqJ4zb3smaV3EFYPggtF9cEQvv_BtBR+Cw@mail.gmail.com>
Date: Mon, 13 Jan 2025 16:27:00 +0800
From: wzs <wangzhengshu39@...il.com>
To: Doug Anderson <dianders@...omium.org>
Cc: tglx@...utronix.de, liusong@...ux.alibaba.com, akpm@...ux-foundation.org, 
	pmladek@...e.com, kernelfans@...il.com, deller@....de, npiggin@...il.com, 
	tsbogend@...ha.franken.de, James.Bottomley@...senpartnership.com, 
	jan.kiszka@...mens.com, linux-kernel@...r.kernel.org, 
	linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, yaoma@...ux.alibaba.com
Subject: Re: watchdog: BUG: soft lockup

Thanks for the tip!

Doug Anderson <dianders@...omium.org> 于2025年1月9日周四 01:33写道：
>
> Hi,
>
> On Sun, Dec 22, 2024 at 10:32 PM wzs <wangzhengshu39@...il.com> wrote:
> >
> > Hello,
> > when fuzzing the Linux kernel,
> > I triggered many "watch: BUG: soft lockup" warnings.
> > I am not sure whether this is an issue with the kernel or with the
> > fuzzing program I ran.
> > (The same fuzzing program, when tested on kernel versions from
> > Linux-6.7.0 to 6.12.0, triggers the 'watchdog: BUG: soft lockup'
> > warning on some versions, while others do not. Linux 6.12.0 is the
> > latest stable release where this error occurs.)
> >
> > The bug information I provided below is from the Linux-6.12.0 kernel.
> > If you need bug information from other versions, I would be happy to provide it.
> >
> > kernel config :https://pastebin.com/i4LPXNAN
> > console output :https://pastebin.com/uKVpvJ78
>
> IMO it's nearly always a bug if userspace can cause the kernel to soft
> lockup. I'd expect this isn't a bug in the soft lockup detector but a
> problem in whatever part of the kernel you're fuzzing. For some
> details of the soft lockup detector, see
> `Documentation/admin-guide/lockup-watchdogs.rst`.
>
> Presumably you're fuzzing the kernel in a way that causes it to enter
> a big loop while preemption is disabled, or something like that.
> Presumably the kernel should be detecting something invalid that
> userspace did and that would keep it from looping so long.
>
> I tried looking at your pastebin and probably what's going on is
> somewhere hidden in there, but unfortunately the beginning of the logs
> are a bit jumbled since it looks like the RCU warning and the soft
> lockup warning happened at about the same time and their stuff is
> jumbled. There's also a lot of tasks to go through. Honestly, it's
> probably less work just to look at whatever you were trying to fuzz to
> help you pinpoint the problem.
>
> I'll also note that you seem to be using KASAN and are running in a
> virtual machine. It's not inconceivable that's contributing to your
> problems. KASAN makes things _a lot_ slower and a VM may be getting
> its time stolen by the host.
>
> -Doug