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

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Message-ID: <50B4C7BD.90807@oracle.com>
Date:	Tue, 27 Nov 2012 09:01:33 -0500
From:	Sasha Levin <sasha.levin@...cle.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,
	avi@...hat.com, fweisbec@...il.com
Subject: Re: [RFC PATCH] Fix abnormal rcu dynticks_nesting values related
 to async page fault

On 11/27/2012 08:07 AM, Gleb Natapov wrote:
> Those rcu_irq_enter()/rcu_irq_exit() were introduced by commit
> c5e015d4949aa665 "KVM guest: exit idleness when handling
> KVM_PV_REASON_PAGE_NOT_PRESENT", but now I am starting to question this
> commit. KVM_PV_REASON_PAGE_NOT_PRESENT should not kick cpu out of
> idleness. kvm_async_pf_task_wait() checks that cpu is idle and calls
> halt if it is. After that commit schedule() may be called between
> rcu_irq_enter()/rcu_irq_exit() which is probably illegal. Paul?

otoh, calling schedule() apparently kicks cpu out of idleness now.


Thanks,
Sasha
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