linux-kernel - Re: WARNING: suspicious RCU usage in idtentry

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Date:   Thu, 28 May 2020 22:19:02 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     paulmck@...nel.org
Cc:     syzbot <syzbot+3ae5eaae0809ee311e75@...kaller.appspotmail.com>,
        Paolo Bonzini <pbonzini@...hat.com>, bp@...en8.de,
        hpa@...or.com, linux-kernel@...r.kernel.org, luto@...nel.org,
        mingo@...nel.org, syzkaller-bugs@...glegroups.com, x86@...nel.org
Subject: Re: WARNING: suspicious RCU usage in idtentry_exit

Paul,

"Paul E. McKenney" <paulmck@...nel.org> writes:
> On Thu, May 28, 2020 at 03:33:44PM +0200, Thomas Gleixner wrote:
>> syzbot <syzbot+3ae5eaae0809ee311e75@...kaller.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

> 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