linux-kernel - Re: [PATCH] drivers/acpi: call rcu_read

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Date:	Sat, 31 Jul 2010 21:46:08 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Julia Lawall <julia@...u.dk>
Cc:	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] drivers/acpi: call rcu_read_unlock in default case

On Sat, Jul 31, 2010 at 10:35:28PM +0200, Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> Adjust the default case so that it benefits from the call to rcu_read_unlock.
> 
> The semantic match that finds this problem is as follows:
> (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @rcu@
> position p1;
> @@
> 
> rcu_read_lock@p1();
> ...
> rcu_read_unlock();
> 
> @@
> position rcu.p1;
> @@
> 
> *rcu_read_lock@p1();
> ... when != rcu_read_unlock();
> // </smpl>

I don't claim to understand the SmPL above, but I do like the patch.

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
>  drivers/acpi/atomicio.c             |   10 ++++++----
>  1 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/acpi/atomicio.c b/drivers/acpi/atomicio.c
> index 8f8bd73..f426010 100644
> --- a/drivers/acpi/atomicio.c
> +++ b/drivers/acpi/atomicio.c
> @@ -267,6 +267,7 @@ EXPORT_SYMBOL_GPL(acpi_post_unmap_gar);
>  static int acpi_atomic_read_mem(u64 paddr, u64 *val, u32 width)
>  {
>  	void __iomem *addr;
> +	int res = 0;
> 
>  	rcu_read_lock();
>  	addr = __acpi_ioremap_fast(paddr, width);
> @@ -284,16 +285,17 @@ static int acpi_atomic_read_mem(u64 paddr, u64 *val, u32 width)
>  		*val = readq(addr);
>  		break;
>  	default:
> -		return -EINVAL;
> +		res = -EINVAL;
>  	}
>  	rcu_read_unlock();
> 
> -	return 0;
> +	return res;
>  }
> 
>  static int acpi_atomic_write_mem(u64 paddr, u64 val, u32 width)
>  {
>  	void __iomem *addr;
> +	int res = 0;
> 
>  	rcu_read_lock();
>  	addr = __acpi_ioremap_fast(paddr, width);
> @@ -311,11 +313,11 @@ static int acpi_atomic_write_mem(u64 paddr, u64 val, u32 width)
>  		writeq(val, addr);
>  		break;
>  	default:
> -		return -EINVAL;
> +		res = -EINVAL;
>  	}
>  	rcu_read_unlock();
> 
> -	return 0;
> +	return res;
>  }
> 
>  /* GAR accessing in atomic (including NMI) or process context */
> --
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