linux-kernel - Re: [PATCH] KVM: Deal with nested sleeps in kvm_vcpu

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Date:   Wed, 30 Nov 2022 17:58:56 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Space Meyer <spm@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     kpsingh@...nel.org
Subject: Re: [PATCH] KVM: Deal with nested sleeps in kvm_vcpu_block()

On 11/30/22 17:19, Space Meyer wrote:
>   bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
>   {
> +	DEFINE_WAIT_FUNC(vcpu_block_wait, woken_wake_function);
>   	struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
>   	bool waited = false;
>   
> @@ -3437,13 +3439,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
>   	preempt_enable();
>   
>   	for (;;) {
> -		set_current_state(TASK_INTERRUPTIBLE);
> -
>   		if (kvm_vcpu_check_block(vcpu) < 0)
>   			break;
>   
>   		waited = true;
> -		schedule();
> +		wait_woken(&vcpu_block_wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
>   	}

Also, this does not work I think, because there is 
add_wait_queue()/remove_wait_queue() pair.  Adding it is not easy 
because KVM is using a struct rcuwait here instead of a wait_queue_t.

Paolo