linux-kernel - Re: [PATCH] drivers/input: Use RCU_INIT

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Message-ID: <20140326203005.GC11013@core.coreip.homeip.net>
Date:	Wed, 26 Mar 2014 13:30:05 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Monam Agarwal <monamagarwal123@...il.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/input: Use RCU_INIT_POINTER(x, NULL) in evdev.c

Hi Monam,

On Sun, Mar 23, 2014 at 11:56:17PM +0530, Monam Agarwal wrote:
> This patch replaces rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x, NULL)
> 
> The rcu_assign_pointer() ensures that the initialization of a structure       
> is carried out before storing a pointer to that structure. 
> And in the case of the NULL pointer, there is no structure to initialize. 
> So, rcu_assign_pointer(p, NULL) can be safely converted to RCU_INIT_POINTER(p, NULL)

Logically speaking we perform assignment, not initialization there.
Since we are not in hot path I think we should leave the code as is.

Thanks.

> 
> Signed-off-by: Monam Agarwal <monamagarwal123@...il.com>
> ---
>  drivers/input/evdev.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index a06e125..fffa107 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -291,7 +291,7 @@ static int evdev_ungrab(struct evdev *evdev, struct evdev_client *client)
>  	if (grab != client)
>  		return  -EINVAL;
>  
> -	rcu_assign_pointer(evdev->grab, NULL);
> +	RCU_INIT_POINTER(evdev->grab, NULL);
>  	synchronize_rcu();
>  	input_release_device(&evdev->handle);
>  
> -- 
> 1.7.9.5
> 

-- 
Dmitry
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