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

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Message-ID: <CAFTL4hyfCt2imzBYW+Sn5QUAwham=ZQ2nNER5Np7Hq4yg1LzxA@mail.gmail.com>
Date:	Tue, 27 Nov 2012 16:56:30 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Gleb Natapov <gleb@...hat.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

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)
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