Re: [PATCH v3] KVM: async_pf: rcu irq exit if not triggered from idle task

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3] KVM: async_pf: rcu irq exit if not triggered from idle task
Date	2017-08-01 12:40 +0200
Message-ID	<u9CKK-2Ig-11@gated-at.bofh.it> (permalink)
References	<u7MXU-4d2-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 27/07/2017 11:05, Wanpeng Li wrote:
> 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 is true, but I think the patch is making things more complex where
it could be simplifying them.  Right now, the "native_safe_halt" branch
is calling rcu_irq_exit/enter but the "schedule" branch is not.  Could
you just pull rcu_irq_exit/enter outside the "if", so that you inform
the RCU subsystem even in the !n.halted case?

Paolo

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Re: [PATCH v3] KVM: async_pf: rcu irq exit if not triggered from idle  task Paolo Bonzini <pbonzini@redhat.com> - 2017-08-01 12:40 +0200
  Re: [PATCH v3] KVM: async_pf: rcu irq exit if not triggered from idle task Wanpeng Li <kernellwp@gmail.com> - 2017-08-01 13:20 +0200
    Re: [PATCH v3] KVM: async_pf: rcu irq exit if not triggered from idle  task Paolo Bonzini <pbonzini@redhat.com> - 2017-08-01 13:40 +0200

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