linux-kernel - Re: [RFC patch 4/7] futex: Add support for attached futexes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160402162632.GQ3448@twins.programming.kicks-ass.net>
Date:	Sat, 2 Apr 2016 18:26:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Darren Hart <darren@...art.com>,
	Ingo Molnar <mingo@...nel.org>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Davidlohr Bueso <dave@...olabs.net>, Chris Mason <clm@...com>,
	Carlos O'Donell <carlos@...hat.com>,
	Torvald Riegel <triegel@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC patch 4/7] futex: Add support for attached futexes

On Sat, Apr 02, 2016 at 11:09:18AM -0000, Thomas Gleixner wrote:
> +/**
> + * hash_local_futex - Return the hash bucket in the task local cache
> + * @uaddr:	The user space address of the futex
> + * @prime:	The prime number for the modulo operation
> + *
> + * That's a primitive hash function, but it turned out to be the most
> + * efficient one for the task local cache as we don't have anything to
> + * mix in like we have for the global hash.
> + */
> +static inline unsigned int
> +hash_local_futex(void __user *uaddr, unsigned int prime)
> +{
> +	return ((unsigned long) uaddr) % prime;
> +}

> +static unsigned int hash_prime(unsigned int size)
> +{
> +	switch(size) {
> +	case   16:
> +	default:   return 13;
> +	case   32: return 31;
> +	case   64: return 61;
> +	case  128: return 127;
> +	case  256: return 251;
> +	case  512: return 509;
> +	case 1024: return 1021;
> +	case 2048: return 2039;
> +	case 4096: return 4093;
> +	}
> +}

One wonders what's wrong with include/linux/hash.h ? It appears to me
hash_ptr() is pretty much what you want, no?