linux-kernel - Re: [PATCH 02/13] EDAC, altera: kill off ACCESS

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Date:   Mon, 9 Oct 2017 18:12:10 -0500
From:   Thor Thayer <thor.thayer@...ux.intel.com>
To:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org
Cc:     Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 02/13] EDAC, altera: kill off ACCESS_ONCE()

On 10/09/2017 01:28 PM, Mark Rutland wrote:
> For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
> preference to ACCESS_ONCE(), and new code is expected to use one of the
> former. So far, there's been no reason to change most existing uses of
> ACCESS_ONCE(), as these aren't currently harmful.
> 
> However, for some features it is necessary to instrument reads and
> writes separately, which is not possible with ACCESS_ONCE(). This
> distinction is critical to correct operation.
> 
> It's possible to transform the bulk of kernel code using the Coccinelle
> script below. However, this doesn't handle comments, leaving references
> to ACCESS_ONCE() instances which have been removed. As a preparatory
> step, this patch converts the Altera EDAC code and comments to use
> {READ,WRITE}_ONCE() consistently.
> 
> ----
> virtual patch
> 
> @ depends on patch @
> expression E1, E2;
> @@
> 
> - ACCESS_ONCE(E1) = E2
> + WRITE_ONCE(E1, E2)
> 
> @ depends on patch @
> expression E;
> @@
> 
> - ACCESS_ONCE(E)
> + READ_ONCE(E)
> ----
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Thor Thayer <thor.thayer@...ux.intel.com>
> ---
>   drivers/edac/altera_edac.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/edac/altera_edac.c b/drivers/edac/altera_edac.c
> index 346c498..11d6419 100644
> --- a/drivers/edac/altera_edac.c
> +++ b/drivers/edac/altera_edac.c
> @@ -175,11 +175,11 @@ static ssize_t altr_sdr_mc_err_inject_write(struct file *file,
>   	/*
>   	 * To trigger the error, we need to read the data back
>   	 * (the data was written with errors above).
> -	 * The ACCESS_ONCE macros and printk are used to prevent the
> +	 * The READ_ONCE macros and printk are used to prevent the
>   	 * the compiler optimizing these reads out.
>   	 */
> -	reg = ACCESS_ONCE(ptemp[0]);
> -	read_reg = ACCESS_ONCE(ptemp[1]);
> +	reg = READ_ONCE(ptemp[0]);
> +	read_reg = READ_ONCE(ptemp[1]);
>   	/* Force Read */
>   	rmb();
>   
> @@ -618,7 +618,7 @@ static ssize_t altr_edac_device_trig(struct file *file,
>   	for (i = 0; i < (priv->trig_alloc_sz / sizeof(*ptemp)); i++) {
>   		/* Read data so we're in the correct state */
>   		rmb();
> -		if (ACCESS_ONCE(ptemp[i]))
> +		if (READ_ONCE(ptemp[i]))
>   			result = -1;
>   		/* Toggle Error bit (it is latched), leave ECC enabled */
>   		writel(error_mask, (drvdata->base + priv->set_err_ofst));
> @@ -635,7 +635,7 @@ static ssize_t altr_edac_device_trig(struct file *file,
>   
>   	/* Read out written data. ECC error caused here */
>   	for (i = 0; i < ALTR_TRIGGER_READ_WRD_CNT; i++)
> -		if (ACCESS_ONCE(ptemp[i]) != i)
> +		if (READ_ONCE(ptemp[i]) != i)
>   			edac_printk(KERN_ERR, EDAC_DEVICE,
>   				    "Read doesn't match written data\n");
>   
> 

Tested on Cyclone5 and Arria10. Thanks!
Acked-by: Thor Thayer <thor.thayer@...ux.intel.com>