linux-kernel - Re: [PATCH 0/3] 64-bit futexes: Intro

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 for Android: free password hash cracker in your pocket

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

Date:	Fri, 30 May 2008 20:14:35 -0700
From:	Ulrich Drepper <drepper@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mtk.manpages@...il.com
Subject: Re: [PATCH 0/3] 64-bit futexes: Intro

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Linus Torvalds wrote:
> We've had a 32-bit rwsemaphore in the kernel for a *long* time.

You misread what I wrote.

Semaphores are fine.  The problem are reader/writer locks where we need
three counters and some flags.  It is absolutely not acceptable to limit
the number of threads to 512 to make this fit.

> I think it's totally stupid for glibc to even *try* to do something like 
> this, since almost nobody will have a kernel with 64-bit futex support for 
> a long time in the wild anyway. So you need to support a 32-bit semaphore 
> in practice, and it's been done before.

Again, misread.  This is not functionality which is not available.
Semaphores are *of course* fine with 32 bits.  And there is a
reader/writer lock implementation.  It is just very slow compared to
what is possible.  The transition between systems miss the 64-bit
support and those which have it is completely transparent.  The same
glibc binary will work for both.

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)

iEYEARECAAYFAkhAwpsACgkQ2ijCOnn/RHS7PACdGvdgI9pv+IcsSPkXPVwFJ5ZF
YNQAn01fm1wEc4EI/fwOVuM57XtCy9Dq
=LcpJ
-----END PGP SIGNATURE-----
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/