Re: WARNING: suspicious RCU usage in idtentry_exit

Paul E. McKenney
2020-05-28T20:48:49Z

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