[02/13] EDAC, altera: kill off ACCESS_ONCE()

Message ID 1507573730-8083-3-git-send-email-mark.rutland@arm.com
State New
Headers show
Series
  • Preparatory work to kill off ACCESS_ONCE()
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Commit Message

Mark Rutland Oct. 9, 2017, 6:28 p.m.
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@arm.com>

Cc: Borislav Petkov <bp@alien8.de>
Cc: Thor Thayer <thor.thayer@linux.intel.com>
---
 drivers/edac/altera_edac.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

-- 
1.9.1

Comments

Thor Thayer Oct. 9, 2017, 11:12 p.m. | #1
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@arm.com>

> Cc: Borislav Petkov <bp@alien8.de>

> Cc: Thor Thayer <thor.thayer@linux.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@linux.intel.com>
Mark Rutland Oct. 10, 2017, 9:30 a.m. | #2
On Mon, Oct 09, 2017 at 06:12:10PM -0500, Thor Thayer wrote:
> On 10/09/2017 01:28 PM, Mark Rutland wrote:

> >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@linux.intel.com>


Thanks, that's much appreciated!

Mark.

Patch

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");