linux-kernel - Re: [PATCH] task containersv11 add tasks file interface fix for cpusets

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]

Date:	Wed, 3 Oct 2007 11:10:58 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Paul Jackson" <pj@....com>
Cc:	akpm@...ux-foundation.org, nickpiggin@...oo.com.au,
	a.p.zijlstra@...llo.nl, serue@...ibm.com, clg@...ibm.com,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
	rientjes@...gle.com, svaidy@...ux.vnet.ibm.com, xemul@...nvz.org,
	containers@...ts.osdl.org, balbir@...ux.vnet.ibm.com
Subject: Re: [PATCH] task containersv11 add tasks file interface fix for cpusets

On 10/3/07, Paul Jackson <pj@....com> wrote:
>
> Yes, something in user space has to do it.  It's part of the
> kernel-user cpuset API.  If you change a cpuset's 'cpus', then
> you have to rewrite each pid in its 'tasks' file back to that
> 'tasks' file in order to get that 'cpus' change to be applied
> to the task struct cpus_allowed of each task, and thereby visible
> to the scheduler.

What's the rationale for this?

Given that later in cpusets.txt you say:

>If hotplug functionality is used
>to remove all the CPUs that are currently assigned to a cpuset,
>then the kernel will automatically update the cpus_allowed of all
>tasks attached to CPUs in that cpuset to allow all CPUs

why can't the same thing be done when changing the 'cpus' file manually.

What's wrong with, in update_cpumask(), doing a loop across all
members of the cgroup and updating their cpus_allowed fields?

The existing cpusets API is broken, since a new child can always be
forked between reading the tasks file and doing the writes.

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/