linux-kernel - Re: BUG: kernel NULL pointer dereference from check_preempt

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Message-ID: <20200605105614.GC2948@hirez.programming.kicks-ass.net>
Date:   Fri, 5 Jun 2020 12:56:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: BUG: kernel NULL pointer dereference from check_preempt_wakeup()

On Fri, Jun 05, 2020 at 12:38:59PM +0200, Peter Zijlstra wrote:
> On Thu, Jun 04, 2020 at 03:54:45PM -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > I get the splat below at a rate of roughly two per thirty hours when
> > running rcutorture scenario TREE03 on x86 at the June 3rd mainline commit:
> > 
> > cb8e59cc8720 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next")
> > 
> > Running 140 hours of this same scenario at the following June 2nd mainline
> > commit shows no errors:
> > 
> > d9afbb350990 ("Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security")
> > 
> > I have started a bisection, but it is likely to take several days to
> > complete.  I am looking at ways of speeding this up, but in the meantime,
> > I figured that I should check to see if others are also encountering this.
> > 
> > Thoughts?
> 
> I think this shows there's a boo-boo with the IPI patches. I've not
> managed to reproduce, but I'll give them another hard look.
> 
> Would you have a .config for me? My compiler's check_preempt_wakeup
> isn't anywhere near 0x180 bytes long. I'm thiknig you have
> instrumentation enabled, KCSAN?

n/m, I was looking at the wrong function.. let me go puzzle.