linux-kernel - Re: [PATCH v1 02/14] futex: Extend the FUTEX2 flags

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Date:   Mon, 31 Jul 2023 18:25:48 +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 02/14] futex: Extend the FUTEX2 flags

On Mon, Jul 31, 2023 at 06:11:27PM +0200, Thomas Gleixner wrote:
> On Fri, Jul 21 2023 at 12:22, Peter Zijlstra wrote:
> > +#define FUTEX2_8		0x00
> > +#define FUTEX2_16		0x01
> >  #define FUTEX2_32		0x02
> > -			/*	0x04 */
> > +#define FUTEX2_64		0x03
> > +#define FUTEX2_NUMA		0x04
> >  			/*	0x08 */
> >  			/*	0x10 */
> >  			/*	0x20 */
> > --- a/kernel/futex/syscalls.c
> > +++ b/kernel/futex/syscalls.c
> > @@ -183,7 +183,7 @@ SYSCALL_DEFINE6(futex, u32 __user *, uad
> >  	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
> >  }
> >  
> > -#define FUTEX2_MASK (FUTEX2_32 | FUTEX2_PRIVATE)
> > +#define FUTEX2_MASK (FUTEX2_64 | FUTEX2_PRIVATE)
> >  
> >  /**
> >   * futex_parse_waitv - Parse a waitv array from userspace
> > @@ -207,7 +207,12 @@ static int futex_parse_waitv(struct fute
> >  		if ((aux.flags & ~FUTEX2_MASK) || aux.__reserved)
> >  			return -EINVAL;
> 
> With the above aux.flags with FUTEX2_32 set will result in -EINVAL. I
> don't think that's intentional.

FUTEX2_8     0
FUTEX2_16    1
FUTEX2_32    2
FUTEX2_64    3

Therefore FUTEX2_64, when used as a mask, includes then all.

Arnd suggested adding FUTEX2_SIZE_MASK or something. And I initially had
something like that, but pulled it for not wanting to pullute the uabi.

Can easily add back.