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

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

Message-ID: <4840D63F.2090407@redhat.com>
Date:	Fri, 30 May 2008 21:38:23 -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:
> Is it possible? I dunno.

Once again not without limitations which are too low.  The main problem
is that there is far more information needed on the reader side.  There
are two counters and a number of bits for state information.  Which
means the counters can be at most 14 bits in size.

A counter this low also means I cannot unconditionally increment them
(since there can be more than 2^14 threads sharing one page).  This
means you get in the cache line race I described in the last mail.  You
first have to load a word and then perform a the write operation while
at the same time other threads competing with you for the same cache line.

> I personally suspect it is. I also suspect you 
> didn't even try.

I have to disappoint you.  I thought of that and had to reject it.

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

iEYEARECAAYFAkhA1j8ACgkQ2ijCOnn/RHTUXQCgnkUy6PNSuUI4O6BD4abxqqKr
PzMAn2qcvrXGM4qrhOytk1Yie0BsMeVa
=zvxZ
-----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/