linux-kernel - Re: [PATCH] KVM: async_pf: Fix rcu_irq

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Message-ID: <CANRm+Cxsbwo8R37f8go3kjTK52CFdce2j68s7RfdtHahKNqk+Q@mail.gmail.com>
Date:   Thu, 8 Jun 2017 16:00:44 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] KVM: async_pf: Fix rcu_irq_enter/exit() usage

2017-06-07 22:24 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>
>
> On 07/06/2017 16:10, Wanpeng Li wrote:
>> 2017-06-07 21:05 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>>>
>>>
>>> On 07/06/2017 14:04, Wanpeng Li wrote:
>>>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>>>
>>>> Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault)
>>>> adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs
>>>> when needed, to protect the code that needs use rcu. There is no need to call
>>>> this pairs if async page fault is not triggered from idle task.
>>>>
>>>> This patch fixes it by rcu irq exit if it is not triggered from idle task to
>>>> avoid rcu hang after schedule() in the for loop.
>>>
>>> How does the bug manifest?
>>
>> Just by codes review.
>
> So it's just code cleanup?

Yeah, this should be a cleanup and I will update the patch
description. Actually, I observe a hang due to async pf injected to L2
which should be injected to L1, then tasks hang in L1 due to missing
PAGE_READY async_pfs.

Regards,
Wanpeng Li