Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
To:     Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch] futex: Cure exit race
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
 format=flowed
Content-Transfer-Encoding: 7bit
Date:   Wed, 19 Dec 2018 14:29:10 +0100
From:   Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Stefan Liebler <stli@linux.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Darren Hart <dvhart@infradead.org>,
        Ingo Molnar <mingo@kernel.org>
In-Reply-To: <alpine.DEB.2.21.1812172239090.1660@nanos.tec.linutronix.de>
References: <20181210152311.986181245@linutronix.de>
 <20181210160205.GQ5289@hirez.programming.kicks-ass.net>
 <alpine.DEB.2.21.1812101824070.1667@nanos.tec.linutronix.de>
 <20181212090418.GT5289@hirez.programming.kicks-ass.net>
 <alpine.DEB.2.21.1812172239090.1660@nanos.tec.linutronix.de>
Message-ID: <539c47359b37a5b6b9177da823be45d6@dl.linutronix.de>
User-Agent: html based client
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2018-12-18 10:31, Thomas Gleixner wrote:
> On Wed, 12 Dec 2018, Peter Zijlstra wrote:
>> On Mon, Dec 10, 2018 at 06:43:51PM +0100, Thomas Gleixner wrote:
>> @@ -806,6 +806,8 @@ void __noreturn do_exit(long code)
>>  		 * task into the wait for ever nirwana as well.
>>  		 */
>>  		tsk->flags |= PF_EXITPIDONE;
>> +		smp_mb();
>> +		wake_up_bit(&tsk->flags, 3 /* PF_EXITPIDONE */);
>
> Using ilog2(PF_EXITPIDONE) spares that horrible inline comment and 
> more
> importantly selects the right bit. 0x04 is bit 2 ....

Plus wake_up_bit() and wait_on_bit() want an unsigned long, but 
tsk->flags is
unsigned int....

Moar staring....