linux-kernel - Re: [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to async page fault

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Date:	Tue, 27 Nov 2012 18:39:10 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Li Zhong <zhong@...ux.vnet.ibm.com>,
	linux-next list <linux-next@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, paulmck@...ux.vnet.ibm.com,
	sasha.levin@...cle.com, avi@...hat.com
Subject: Re: [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to
 async page fault

On Tue, Nov 27, 2012 at 04:56:30PM +0100, Frederic Weisbecker wrote:
> 2012/11/27 Gleb Natapov <gleb@...hat.com>:
> > For KVM_PV_REASON_PAGE_NOT_PRESENT it behaves like an exception.
> 
> Ok.
> There seem to be a bug in kvm_async_pf_task_wait(). Using
> idle_cpu(cpu) to find out if the current task is the idle task may not
> work if there is pending wake up. Me may schedule another task but
> when that other task sleeps later we can't schedule back to idle until
> the fault is completed.
> 
> The right way is to use is_idle_task(current)
But if there is pending wake up then scheduling to the waked up task is
exactly what we want.

--
			Gleb.
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