linux-kernel - Re: [PATCH 1/3] cgroup: convert open-coded mutex_lock(&cgroup_mutex) calls into cgroup

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: <6599ad830901181737m1d04bb85t7bb0b48e925733a6@mail.gmail.com>
Date:	Sun, 18 Jan 2009 17:37:21 -0800
From:	Paul Menage <menage@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	miaox@...fujitsu.com, maxk@...lcomm.com,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/3] cgroup: convert open-coded mutex_lock(&cgroup_mutex) 
	calls into cgroup_lock() calls

On Sun, Jan 18, 2009 at 1:10 AM, Ingo Molnar <mingo@...e.hu> wrote:
> this just changes over a clean mutex call to a wrapped lock/unlock
> sequence that has higher overhead in the common case.
>
> We should do the exact opposite, we should change this opaque API:
>
>  void cgroup_lock(void)
>  {
>         mutex_lock(&cgroup_mutex);
>  }
>
> To something more explicit (and more maintainable) like:

I disagree - cgroup_mutex is a very coarse lock that can be held for
pretty long periods of time by the cgroups framework, and should never
be part of any fastpath code. So the overhead of a function call
should be irrelevant.

The change that you're proposing would send the message that
cgroup_mutex_lock(&cgroup_mutex) is appropriate to use in a
performance-sensitive function, when in fact we want to discourage
such code from taking this lock and instead use more appropriately
fine-grained locks.

Paul
--
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/