linux-kernel - Re: [patch] futex: Cure exit race

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Message-ID: <539c47359b37a5b6b9177da823be45d6@dl.linutronix.de>
Date:   Wed, 19 Dec 2018 14:29:10 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Stefan Liebler <stli@...ux.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Darren Hart <dvhart@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [patch] futex: Cure exit race

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....