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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: syzbot <syzbot+3ae5eaae0809ee311e75@syzkaller.appspotmail.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	bp@alien8.de, hpa@zytor.com, linux-kernel@vger.kernel.org,
	luto@kernel.org, mingo@kernel.org,
	syzkaller-bugs@googlegroups.com, x86@kernel.org
Subject: Re: WARNING: suspicious RCU usage in idtentry_exit
Date: Thu, 28 May 2020 13:48:39 -0700	[thread overview]
Message-ID: <20200528204839.GR2869@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <878shbols9.fsf@nanos.tec.linutronix.de>

On Thu, May 28, 2020 at 10:19:02PM +0200, Thomas Gleixner wrote:
> Paul,
> 
> "Paul E. McKenney" <paulmck@kernel.org> writes:
> > On Thu, May 28, 2020 at 03:33:44PM +0200, Thomas Gleixner wrote:
> >> syzbot <syzbot+3ae5eaae0809ee311e75@syzkaller.appspotmail.com> writes:
> >> Weird. I have no idea how that thing is an EQS here.
> >
> > No argument on the "Weird" part!  ;-)
> >
> > Is this a NO_HZ_FULL=y kernel?
> 
> No, it has only NO_HZ_IDLE.
> 
>   https://syzkaller.appspot.com/x/.config?x=47b0740d89299c10

OK, from the .config, another suggestion is to build the kernel
with CONFIG_RCU_EQS_DEBUG=y.  This still requires that this issue be
reproduced, but it might catch the problem earlier.

> > If so, one possibility is that the call
> > to rcu_user_exit() went missing somehow.  If not, then RCU should have
> > been watching userspace execution.
> >
> > Again, the only thing I can think of (should this prove to be
> > reproducible) is the rcu_dyntick trace event.
> 
> :)
> 
> Thanks,
> 
>         tglx

							Thanx, Paul

  reply	other threads:[~2020-05-28 20:48 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-26  3:54 WARNING: suspicious RCU usage in idtentry_exit syzbot
2020-05-28 13:33 ` Thomas Gleixner
2020-05-28 16:11   ` Paul E. McKenney
2020-05-28 20:19     ` Thomas Gleixner
2020-05-28 20:48       ` Paul E. McKenney [this message]
2020-05-29  6:20         ` Dmitry Vyukov
2020-05-29  8:51           ` Thomas Gleixner
2020-05-29 14:05           ` Paul E. McKenney
2020-05-29 14:32             ` Dmitry Vyukov
2020-05-29 16:07               ` Paul E. McKenney
2020-07-31  9:23   ` [tip: core/rcu] lockdep: Complain only once about RCU in extended quiescent state tip-bot2 for Paul E. McKenney

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