linux-kernel - Re: [RFC][PATCH 07/10] futex: Implement FUTEX2

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Date:   Fri, 14 Jul 2023 17:22:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de, axboe@...nel.dk
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        dvhart@...radead.org, dave@...olabs.net, andrealmeid@...lia.com,
        Andrew Morton <akpm@...ux-foundation.org>, urezki@...il.com,
        hch@...radead.org, lstoakes@...il.com,
        Arnd Bergmann <arnd@...db.de>, linux-api@...r.kernel.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        malteskarupke@....de
Subject: Re: [RFC][PATCH 07/10] futex: Implement FUTEX2_NUMA

On Fri, Jul 14, 2023 at 03:39:06PM +0200, Peter Zijlstra wrote:
> +	/*
> +	 * Encode the futex size in the offset. This makes cross-size
> +	 * wake-wait fail -- see futex_match().
> +	 *
> +	 * NOTE that cross-size wake-wait is fundamentally broken wrt
> +	 * FLAGS_NUMA but could possibly work for !NUMA.
> +	 */
> +	key->both.offset |= FUT_OFF_SIZE * (flags & FLAGS_SIZE_MASK);

this wee bit should've gone in patch 9.