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

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Message-ID: <20230712092514.GE3100107@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Jul 2023 11:25:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jens Axboe <axboe@...nel.dk>
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 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 ?!?