linux-kernel - Re: [PATCH 2/9] rcu: Fixup noinstr warnings

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Message-ID: <20200615155220.GE2723@paulmck-ThinkPad-P72>
Date:   Mon, 15 Jun 2020 08:52:20 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, x86@...nel.org, elver@...gle.com,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        will@...nel.org, dvyukov@...gle.com, glider@...gle.com,
        andreyknvl@...gle.com
Subject: Re: [PATCH 2/9] rcu: Fixup noinstr warnings

On Mon, Jun 15, 2020 at 05:30:52PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 03, 2020 at 09:46:00AM -0700, Paul E. McKenney wrote:
> 
> > >  	// RCU is now watching.  Better not be in an extended quiescent state!
> > >  	rcu_dynticks_task_trace_exit();  // After ->dynticks update!
> > >  	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> > >  		     !(seq & RCU_DYNTICK_CTRL_CTR));
> > >  	if (seq & RCU_DYNTICK_CTRL_MASK) {
> > > -		atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
> > > +		arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
> > 
> > This one is gone in -rcu.
> 
> I'm still seeing that in mainline, was that removal scheduled for next
> round?

Yes.  Unlike the few commits following it, this commit seems to work
fine even with the recent changes in mainline.

> > >  		smp_mb__after_atomic(); /* _exit after clearing mask. */
> > >  	}
> > >  }
> 
> What shall we do with this patch?

I plan to submit it to the v5.9 merge window.  Do you need it to get
to mainline earlier?

							Thanx, Paul