linux-kernel - Re: [PATCH] eventfd: Replace rcu_assign_pointer() with RCU_INIT

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Date:	Mon, 18 Aug 2014 17:06:16 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andreea-Cristina Bernat <bernat.ada@...il.com>, gleb@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
CC:	paulmck@...ux.vnet.ibm.com, monamagarwal123@...il.com
Subject: Re: [PATCH] eventfd: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

Il 18/08/2014 17:01, Andreea-Cristina Bernat ha scritto:
> The uses of "rcu_assign_pointer()" are NULLing out the pointers.
> According to RCU_INIT_POINTER()'s block comment:
> "1.   This use of RCU_INIT_POINTER() is NULLing out the pointer"
> it is better to use it instead of rcu_assign_pointer() because it has a
> smaller overhead.
> 
> The following Coccinelle semantic patch was used:
> @@
> @@
> 
> - rcu_assign_pointer
> + RCU_INIT_POINTER
>   (..., NULL)
> 
> Signed-off-by: Andreea-Cristina Bernat <bernat.ada@...il.com>
> ---
>  virt/kvm/eventfd.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 20c3af7..a49130f 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -278,7 +278,7 @@ static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
>  	struct kvm_kernel_irq_routing_entry *e;
>  
>  	if (irqfd->gsi >= irq_rt->nr_rt_entries) {
> -		rcu_assign_pointer(irqfd->irq_entry, NULL);
> +		RCU_INIT_POINTER(irqfd->irq_entry, NULL);
>  		return;
>  	}
>  
> @@ -287,7 +287,7 @@ static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
>  		if (e->type == KVM_IRQ_ROUTING_MSI)
>  			rcu_assign_pointer(irqfd->irq_entry, e);
>  		else
> -			rcu_assign_pointer(irqfd->irq_entry, NULL);
> +			RCU_INIT_POINTER(irqfd->irq_entry, NULL);
>  	}
>  }
>  
> @@ -473,7 +473,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
>  			 * It is paired with synchronize_srcu done by caller
>  			 * of that function.
>  			 */
> -			rcu_assign_pointer(irqfd->irq_entry, NULL);
> +			RCU_INIT_POINTER(irqfd->irq_entry, NULL);
>  			irqfd_deactivate(irqfd);
>  		}
>  	}
> 

Hi, this patch actually had been submitted already last March.  It
slipped through the cracks.  I'm now applying both of Monam Agarwal's
RCU_INIT_POINTER patches.  Sorry. :)

Thanks,

Paolo
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