Date: Fri, 27 Feb 2015 12:54:28 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Darren Hart <darren@dvhart.com>, Thomas Gleixner <tglx@linutronix.de>,
        Jerome Marchand <jmarchan@redhat.com>,
        Larry Woodman <lwoodman@redhat.com>, Mateusz Guzik <mguzik@redhat.com>,
        linux-kernel@vger.kernel.org, Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Pavel Emelyanov <xemul@parallels.com>
Subject: Re: [PATCH 1/1] futex: don't spin waiting for PF_EXITING ->
 PF_EXITPIDONE transition
Message-ID: <20150227115428.GA24151@twins.programming.kicks-ass.net>
References: <20150202140515.GA26398@redhat.com>
 <20150216201313.GA18246@redhat.com>
 <20150216201336.GB18246@redhat.com>
 <20150227095240.GO5029@twins.programming.kicks-ass.net>
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On Fri, Feb 27, 2015 at 10:52:40AM +0100, Peter Zijlstra wrote:
> On Mon, Feb 16, 2015 at 09:13:36PM +0100, Oleg Nesterov wrote:
> 
> > diff --git a/kernel/futex.c b/kernel/futex.c
> > index b101381..c1104a8 100644
> > +++ b/kernel/futex.c
> > @@ -716,11 +716,13 @@ void exit_pi_state_list(struct task_struct *curr)
> >  
> >  	if (!futex_cmpxchg_enabled)
> >  		return;
> > +
> >  	/*
> > +	 * attach_to_pi_owner() can no longer add the new entry. But
> > +	 * we have to be careful versus waiters unqueueing themselves.
> >  	 */
> > +	curr->flags |= PF_EXITPIDONE;
> > +
> >  	raw_spin_lock_irq(&curr->pi_lock);
> >  	while (!list_empty(head)) {
> >  
> 
> Should we not set PF_EXITPIDONE _inside_ the pi_lock? To properly
> serialize against the below check?

It does not matter, n/m.
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