Subject: Re: [PATCH 04/40] sched: implement __set_cpus_allowed()
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: torvalds@linux-foundation.org, mingo@elte.hu, awalls@radix.net,
       linux-kernel@vger.kernel.org, jeff@garzik.org,
       akpm@linux-foundation.org, jens.axboe@oracle.com, rusty@rustcorp.com.au,
       cl@linux-foundation.org, dhowells@redhat.com, arjan@linux.intel.com,
       avi@redhat.com, johannes@sipsolutions.net, andi@firstfloor.org,
       Mike Galbraith <efault@gmx.de>
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Date: Tue, 19 Jan 2010 09:37:02 +0100
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On Tue, 2010-01-19 at 10:07 +0900, Tejun Heo wrote:
> 
> It's also necessary to guarantee forward progress during CPU_DOWN.
> The problem with kthread_bind() is that it's not synchronized against
> CPU hotplug operations.  It needs outer synchronization like calling
> it directly from CPU_DOWN_PREP.  I guess it's doable but I think it
> would be better to simply share the backend implementation between
> set_cpus_allowed_ptr() and kthread_bind().

OK, so you're saying you need to migrate the rescue thread during
cpu-down. That thread is guaranteed sleeping right, if it were not it'd
not be elegible to run on our dying cpu. Hence kthread_bind() ought to
just work, no?

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