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From: Mark Rutland <mark.rutland@arm.com>
To: linux-kernel@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Thierry Reding <thierry.reding@gmail.com>
Subject: [PATCH 03/13] firmware/ivc: kill off ACCESS_ONCE()
Date: Mon,  9 Oct 2017 19:28:40 +0100	[thread overview]
Message-ID: <1507573730-8083-4-git-send-email-mark.rutland@arm.com> (raw)
In-Reply-To: <1507573730-8083-1-git-send-email-mark.rutland@arm.com>

workqueue: kill off ACCESS_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 Tegra IVC 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: Jonathan Hunter <jonathanh@nvidia.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
---
 drivers/firmware/tegra/ivc.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/firmware/tegra/ivc.c b/drivers/firmware/tegra/ivc.c
index a01461d..00de793 100644
--- a/drivers/firmware/tegra/ivc.c
+++ b/drivers/firmware/tegra/ivc.c
@@ -99,11 +99,11 @@ static inline bool tegra_ivc_empty(struct tegra_ivc *ivc,
 {
 	/*
 	 * This function performs multiple checks on the same values with
-	 * security implications, so create snapshots with ACCESS_ONCE() to
+	 * security implications, so create snapshots with READ_ONCE() to
 	 * ensure that these checks use the same values.
 	 */
-	u32 tx = ACCESS_ONCE(header->tx.count);
-	u32 rx = ACCESS_ONCE(header->rx.count);
+	u32 tx = READ_ONCE(header->tx.count);
+	u32 rx = READ_ONCE(header->rx.count);
 
 	/*
 	 * Perform an over-full check to prevent denial of service attacks
@@ -124,8 +124,8 @@ static inline bool tegra_ivc_empty(struct tegra_ivc *ivc,
 static inline bool tegra_ivc_full(struct tegra_ivc *ivc,
 				  struct tegra_ivc_header *header)
 {
-	u32 tx = ACCESS_ONCE(header->tx.count);
-	u32 rx = ACCESS_ONCE(header->rx.count);
+	u32 tx = READ_ONCE(header->tx.count);
+	u32 rx = READ_ONCE(header->rx.count);
 
 	/*
 	 * Invalid cases where the counters indicate that the queue is over
@@ -137,8 +137,8 @@ static inline bool tegra_ivc_full(struct tegra_ivc *ivc,
 static inline u32 tegra_ivc_available(struct tegra_ivc *ivc,
 				      struct tegra_ivc_header *header)
 {
-	u32 tx = ACCESS_ONCE(header->tx.count);
-	u32 rx = ACCESS_ONCE(header->rx.count);
+	u32 tx = READ_ONCE(header->tx.count);
+	u32 rx = READ_ONCE(header->rx.count);
 
 	/*
 	 * This function isn't expected to be used in scenarios where an
@@ -151,8 +151,8 @@ static inline u32 tegra_ivc_available(struct tegra_ivc *ivc,
 
 static inline void tegra_ivc_advance_tx(struct tegra_ivc *ivc)
 {
-	ACCESS_ONCE(ivc->tx.channel->tx.count) =
-		ACCESS_ONCE(ivc->tx.channel->tx.count) + 1;
+	WRITE_ONCE(ivc->tx.channel->tx.count,
+		   READ_ONCE(ivc->tx.channel->tx.count) + 1);
 
 	if (ivc->tx.position == ivc->num_frames - 1)
 		ivc->tx.position = 0;
@@ -162,8 +162,8 @@ static inline void tegra_ivc_advance_tx(struct tegra_ivc *ivc)
 
 static inline void tegra_ivc_advance_rx(struct tegra_ivc *ivc)
 {
-	ACCESS_ONCE(ivc->rx.channel->rx.count) =
-		ACCESS_ONCE(ivc->rx.channel->rx.count) + 1;
+	WRITE_ONCE(ivc->rx.channel->rx.count,
+		   READ_ONCE(ivc->rx.channel->rx.count) + 1);
 
 	if (ivc->rx.position == ivc->num_frames - 1)
 		ivc->rx.position = 0;
@@ -428,7 +428,7 @@ int tegra_ivc_notified(struct tegra_ivc *ivc)
 
 	/* Copy the receiver's state out of shared memory. */
 	tegra_ivc_invalidate(ivc, ivc->rx.phys + offset);
-	state = ACCESS_ONCE(ivc->rx.channel->tx.state);
+	state = READ_ONCE(ivc->rx.channel->tx.state);
 
 	if (state == TEGRA_IVC_STATE_SYNC) {
 		offset = offsetof(struct tegra_ivc_header, tx.count);
-- 
1.9.1

  parent reply	other threads:[~2017-10-09 18:30 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-09 18:28 [PATCH 00/13] Preparatory work to kill off ACCESS_ONCE() Mark Rutland
2017-10-09 18:28 ` [PATCH 01/13] dm integrity: " Mark Rutland
2017-10-09 18:28 ` [PATCH 02/13] EDAC, altera: " Mark Rutland
2017-10-09 23:12   ` Thor Thayer
2017-10-10  9:30     ` Mark Rutland
2017-10-09 18:28 ` Mark Rutland [this message]
2017-10-09 18:28 ` [PATCH 04/13] fs: dcache: " Mark Rutland
2017-10-09 18:28 ` [PATCH 05/13] fs: ncpfs: " Mark Rutland
2017-10-09 18:28 ` [PATCH 06/13] media: dvb_ringbuffer: " Mark Rutland
2017-10-09 18:28 ` [PATCH 07/13] net: netlink/netfilter: " Mark Rutland
2017-10-09 18:28 ` [PATCH 08/13] net/ipv4/tcp_input.c: " Mark Rutland
2017-10-09 19:03   ` Mark Rutland
2017-10-09 18:28 ` [PATCH 09/13] net: average: " Mark Rutland
2017-10-10  9:28   ` Mark Rutland
2017-10-09 18:28 ` [PATCH 10/13] samples: mic/mpssd/mpssd.c: " Mark Rutland
2017-10-09 18:28 ` [PATCH 11/13] selftests/powerpc: " Mark Rutland
2017-10-10  0:45   ` Michael Ellerman
2017-10-10  9:32     ` Mark Rutland
2017-10-09 18:28 ` [PATCH 12/13] workqueue: " Mark Rutland
2017-10-10 14:06   ` Tejun Heo
2017-10-10 16:21     ` Mark Rutland
2017-10-09 18:28 ` [PATCH 13/13] rcutorture: formal: prepare for ACCESS_ONCE() removal Mark Rutland
2017-10-09 19:51   ` Paul E. McKenney
2017-10-10  9:54     ` Mark Rutland
2017-10-10 12:47       ` Paul E. McKenney
2017-10-10 12:50         ` Mark Rutland
2017-10-10 14:52           ` Paul E. McKenney
2017-10-10 16:24             ` Mark Rutland
2017-10-10 16:35               ` Paul E. McKenney
2017-10-10 16:27             ` Joe Perches
2017-10-10 16:35               ` Paul E. McKenney
2017-10-10 16:41               ` Mark Rutland
2017-10-10 16:57                 ` [Ksummit-discuss] " Joe Perches
2017-10-10 16:57                   ` Joe Perches
2017-10-10 17:06                   ` [Ksummit-discuss] " Mark Rutland
2017-10-10 17:06                     ` Mark Rutland
2017-10-09 20:02 ` [PATCH 00/13] Preparatory work to kill off ACCESS_ONCE() Paul E. McKenney

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