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

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Message-ID: <87mszcm0zw.ffs@tglx>
Date:   Mon, 31 Jul 2023 19:42:11 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>, axboe@...nel.dk
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.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 18:11, 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.

Aargh. This is really nasty to make FUTEX2_64 0x3 and abuse it to test
the flags for validity. Intuitive and obvious is something else.