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Date: Tue, 11 Sep 2018 14:41:29 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Dmitry Safonov <dima@arista.com>
Cc: linux-kernel@vger.kernel.org,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Daniel Axtens <dja@axtens.net>,
        Dmitry Vyukov <dvyukov@google.com>,
        Michael Neuling <mikey@neuling.org>,
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        Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?= <pasik@iki.fi>,
        Peter Hurley <peter@hurleysoftware.com>,
        "Rong, Chen" <rong.a.chen@intel.com>,
        Tan Xiaojun <tanxiaojun@huawei.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        stable@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCHv3 2/6] tty/ldsem: Update waiter->task before waking up
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Message-ID: <20180911054129.GC4065@jagdpanzerIV>
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 <20180911014821.26286-3-dima@arista.com>
 <20180911050449.GB4065@jagdpanzerIV>
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On (09/11/18 14:04), Sergey Senozhatsky wrote:
> >  	for (;;) {
> >  		set_current_state(TASK_UNINTERRUPTIBLE);
> 
> I think that set_current_state() also executes memory barrier. Just
> because it accesses task state.
> 
> > -		if (!waiter.task)
> > +		if (!READ_ONCE(waiter.task))
> >  			break;
> >  		if (!timeout)
> >  			break;

This READ_ONCE(waiter.task) looks interesting. Maybe could be moved
to a loop condition

	while (!READ_ONCE(waiter.task)) {
		...
	}

	-ss