linux-kernel - Re: + work_on_cpu-rewrite-it-to-create-a-kernel-thread-on-demand.patch added to -mm tree

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Message-Id: <20090212124835.2fc41620.akpm@linux-foundation.org>
Date:	Thu, 12 Feb 2009 12:48:35 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	fweisbec@...il.com, mingo@...e.hu, linux-kernel@...r.kernel.org,
	oleg@...hat.com, travis@....com, a.p.zijlstra@...llo.nl,
	mm-commits@...r.kernel.org, rusty@...tcorp.com.au
Subject: Re: +
 work_on_cpu-rewrite-it-to-create-a-kernel-thread-on-demand.patch  added to
 -mm tree

On Thu, 12 Feb 2009 12:38:36 -0800
ebiederm@...ssion.com (Eric W. Biederman) wrote:

> Andrew Morton <akpm@...ux-foundation.org> writes:
> >
> > Series of four patches:
> >
> > - switch cstate.c frmo work_on_cpu to smp_call_function_single()
> >
> > - ditto acpi-cpufreq.c
> >
> > - ditto mce_amd_64.c
> >
> > The final work_on_cpu() caller is pci_call_probe().  I'd like to find a
> > way of removing that callsite as well, so we can finally remove this
> > turkey but for now, just fix the bugs in it:
> 
> As far as I can tell when we are doing the probes we are in a function
> that can sleep, so we should be able to just call set_cpus_allowed to
> remove the need for work_on_cpu in pci_call_probe.  Possibly with a
> save/restore of the allowed cpus.
> 
> Am I missing something?
> 

The problem with set_cpus_allowed() is that some other
suitably-privileged userspace process can come in from the side and
modify your cpus_allowed at any time.

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