linux-kernel - Re: [PATCH v1 09/14] futex: Add sys_futex

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Message-ID: <20230731173856.GQ29590@hirez.programming.kicks-ass.net>
Date:   Mon, 31 Jul 2023 19:38:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     axboe@...nel.dk, 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: [PATCH v1 09/14] futex: Add sys_futex_requeue()

On Mon, Jul 31, 2023 at 07:19:17PM +0200, Thomas Gleixner wrote:
> On Fri, Jul 21 2023 at 12:22, Peter Zijlstra wrote:
> > +/*
> > + * sys_futex_requeue - Requeue a waiter from one futex to another
> > + * @waiters:	array describing the source and destination futex
> > + * @flags:	unused
> > + * @nr_wake:	number of futexes to wake
> > + * @nr_requeue:	number of futexes to requeue
> > + *
> > + * Identical to the traditional FUTEX_CMP_REQUEUE op, except it is part of the
> > + * futex2 family of calls.
> > + */
> > +
> > +SYSCALL_DEFINE4(futex_requeue,
> > +		struct futex_waitv __user *, waiters,
> > +		unsigned int, flags,
> > +		int, nr_wake,
> > +		int, nr_requeue)
> > +{
> > +	struct futex_vector futexes[2];
> > +	u32 cmpval;
> 
> So this is explictely u32. I'm completely confused vs. the 64 bit futex
> size variant enablement earlier in the series by now.

As per the previous email; these patches only enable the syscall part of
64bit futexes, they do not convert the core, and per futex_flags_valid()
(patches 4 and 13), explicitly disallow having FUTEX2_64 set.


-       /* Only 32bit futexes are implemented -- for now */
-       if ((flags & FLAGS_SIZE_MASK) != FLAGS_SIZE_32)
+       /* 64bit futexes aren't implemented -- yet */
+       if ((flags & FLAGS_SIZE_MASK) == FLAGS_SIZE_64)
		return false;