linux-kernel - Re: [PATCH 5/7] futex: make futex_parse

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Date:   Wed, 12 Jul 2023 09:06:35 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com
Subject: Re: [PATCH 5/7] futex: make futex_parse_waitv() available as a helper

On 7/12/23 3:25?AM, Peter Zijlstra wrote:
> On Tue, Jul 11, 2023 at 06:47:03PM -0600, Jens Axboe wrote:
> 
>> Since we now provide a way to pass in a wake handler and data, ensure we
>> use __futex_queue() to avoid having futex_queue() overwrite our wait
>> data.
> 
>> diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
>> index 3471af87cb7d..dfd02ca5ecfa 100644
>> --- a/kernel/futex/waitwake.c
>> +++ b/kernel/futex/waitwake.c
>> @@ -446,7 +446,8 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo
>>  			 * next futex. Queue each futex at this moment so hb can
>>  			 * be unlocked.
>>  			 */
>> -			futex_queue(q, hb);
>> +			__futex_queue(q, hb);
>> +			spin_unlock(&hb->lock);
>>  			continue;
>>  		}
> 
> I'm not following; I even applied all your patches up to this point, but
> futex_queue() still reads:
> 
> static inline void futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
> 	__releases(&hb->lock)
> {
> 	__futex_queue(q, hb);
> 	spin_unlock(&hb->lock);
> }
> 
> How would it be different and overwrite anything ?!?

Good catch, this is a leftover from storing the task/wakeup data
separately. But I got rid of that, so it's stale comment at this point
and we can certainly use futex_queue() here again and drop this hunk.
Will make that edit.

-- 
Jens Axboe