linux-kernel - Re: [PATCH] kfence: Avoid stalling work queue task without allocations

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Message-ID: <20201123112812.19e918b3@gandalf.local.home>
Date:   Mon, 23 Nov 2020 11:28:12 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Marco Elver <elver@...gle.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>, rcu@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH] kfence: Avoid stalling work queue task without
 allocations

On Mon, 23 Nov 2020 16:27:20 +0100
Marco Elver <elver@...gle.com> wrote:

> On Fri, Nov 20, 2020 at 02:27PM -0500, Steven Rostedt wrote:
> > On Thu, 19 Nov 2020 13:53:57 +0100
> > Marco Elver <elver@...gle.com> wrote:
> >   
> > > Running tests again, along with the function tracer
> > > Running tests on all trace events:
> > > Testing all events: 
> > > BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 12s!  
> > 
> > The below patch might be noisy, but can you add it to the kernel that
> > crashes and see if a particular event causes the issue?
> > 
> > [ note I didn't even compile test. I hope it works ;) ]
> > 
> > Perhaps run it a couple of times to see if it crashes on the same set of
> > events each time.  
> 
> Thanks! I have attached the logs of 2 runs. I think one problem here is
> that the enabling of an event doesn't immediately trigger the problem,
> so it's hard to say which one caused it.
> 

I noticed:


[  237.650900] enabling event benchmark_event

In both traces. Could you disable CONFIG_TRACEPOINT_BENCHMARK and see if
the issue goes away. That event kicks off a thread that spins in a tight
loop for some time and could possibly cause some issues.

It still shouldn't break things, we can narrow it down if it is the culprit.

-- Steve