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 18:30:32 +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>:
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 4180a87..636800d 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -113,7 +113,7 @@ void kvm_async_pf_task_wait(u32 token)
>         int cpu, idle;
>
>         cpu = get_cpu();
> -       idle = idle_cpu(cpu);
> +       idle = is_idle_task(current);

I suggest this part goes to a standalone patch.

>         put_cpu();
>
>         spin_lock(&b->lock);
> @@ -247,10 +247,7 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
>                 break;
>         case KVM_PV_REASON_PAGE_NOT_PRESENT:
>                 /* page is swapped out by the host. */
> -               rcu_irq_enter();
> -               exit_idle();
>                 kvm_async_pf_task_wait((u32)read_cr2());
> -               rcu_irq_exit();

Hmm, we still need those above around. I believe we just need to add
rcu_user_exit() in the beginning of that case.
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