linux-kernel - [tip:locking/core] locking/atomics, EDAC/altera: Convert ACCESS_ONCE() to READ_ONCE()/WRITE

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Date:   Wed, 25 Oct 2017 03:16:07 -0700
From:   tip-bot for Mark Rutland <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        mingo@...nel.org, bp@...en8.de, tglx@...utronix.de,
        thor.thayer@...ux.intel.com, peterz@...radead.org, hpa@...or.com,
        paulmck@...ux.vnet.ibm.com, mark.rutland@....com
Subject: [tip:locking/core] locking/atomics, EDAC/altera: Convert
 ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()

Commit-ID:  332efa6374de75c622b782569b16bb50fd722cf5
Gitweb:     https://git.kernel.org/tip/332efa6374de75c622b782569b16bb50fd722cf5
Author:     Mark Rutland <mark.rutland@....com>
AuthorDate: Mon, 23 Oct 2017 14:07:12 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 25 Oct 2017 11:00:56 +0200

locking/atomics, EDAC/altera: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()

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>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Acked-by: Thor Thayer <thor.thayer@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: davem@...emloft.net
Cc: linux-arch@...r.kernel.org
Cc: mpe@...erman.id.au
Cc: shuah@...nel.org
Cc: snitzer@...hat.com
Cc: tj@...nel.org
Cc: viro@...iv.linux.org.uk
Cc: will.deacon@....com
Link: http://lkml.kernel.org/r/1508792849-3115-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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");