[tip:locking/core] locking/atomics, dm-integrity: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()

[tip-bot for Mark Rutland]

Commit-ID:  d3e632f07b6e637d3643081873867ecb6433b2ce
Gitweb:     https://git.kernel.org/tip/d3e632f07b6e637d3643081873867ecb6433b2ce
Author:     Mark Rutland <mark.rutland@xxxxxxx>
AuthorDate: Mon, 23 Oct 2017 14:07:11 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 25 Oct 2017 11:00:55 +0200

locking/atomics, dm-integrity: 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 pick up some uses, including those
in dm-integrity.c. As a preparatory step, this patch converts the driver
to use {READ,WRITE}_ONCE() consistently.

At the same time, this patch adds the missing include of
<linux/compiler.h> necessary for the {READ,WRITE}_ONCE() definitions.

----
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@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: davem@xxxxxxxxxxxxx
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: mpe@xxxxxxxxxxxxxx
Cc: shuah@xxxxxxxxxx
Cc: thor.thayer@xxxxxxxxxxxxxxx
Cc: tj@xxxxxxxxxx
Cc: viro@xxxxxxxxxxxxxxxxxx
Cc: will.deacon@xxxxxxx
Link: http://lkml.kernel.org/r/1508792849-3115-1-git-send-email-paulmck@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 drivers/md/dm-integrity.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-integrity.c b/drivers/md/dm-integrity.c
index 096fe9b..8c5756e 100644
--- a/drivers/md/dm-integrity.c
+++ b/drivers/md/dm-integrity.c
@@ -6,6 +6,7 @@
  * This file is released under the GPL.
  */
 
+#include <linux/compiler.h>
 #include <linux/module.h>
 #include <linux/device-mapper.h>
 #include <linux/dm-io.h>
@@ -80,13 +81,13 @@ struct journal_entry {
 #define journal_entry_tag(ic, je)		((__u8 *)&(je)->last_bytes[(ic)->sectors_per_block])
 
 #if BITS_PER_LONG == 64
-#define journal_entry_set_sector(je, x)		do { smp_wmb(); ACCESS_ONCE((je)->u.sector) = cpu_to_le64(x); } while (0)
+#define journal_entry_set_sector(je, x)		do { smp_wmb(); WRITE_ONCE((je)->u.sector, cpu_to_le64(x)); } while (0)
 #define journal_entry_get_sector(je)		le64_to_cpu((je)->u.sector)
 #elif defined(CONFIG_LBDAF)
-#define journal_entry_set_sector(je, x)		do { (je)->u.s.sector_lo = cpu_to_le32(x); smp_wmb(); ACCESS_ONCE((je)->u.s.sector_hi) = cpu_to_le32((x) >> 32); } while (0)
+#define journal_entry_set_sector(je, x)		do { (je)->u.s.sector_lo = cpu_to_le32(x); smp_wmb(); WRITE_ONCE((je)->u.s.sector_hi, cpu_to_le32((x) >> 32)); } while (0)
 #define journal_entry_get_sector(je)		le64_to_cpu((je)->u.sector)
 #else
-#define journal_entry_set_sector(je, x)		do { (je)->u.s.sector_lo = cpu_to_le32(x); smp_wmb(); ACCESS_ONCE((je)->u.s.sector_hi) = cpu_to_le32(0); } while (0)
+#define journal_entry_set_sector(je, x)		do { (je)->u.s.sector_lo = cpu_to_le32(x); smp_wmb(); WRITE_ONCE((je)->u.s.sector_hi, cpu_to_le32(0)); } while (0)
 #define journal_entry_get_sector(je)		le32_to_cpu((je)->u.s.sector_lo)
 #endif
 #define journal_entry_is_unused(je)		((je)->u.s.sector_hi == cpu_to_le32(-1))
@@ -320,7 +321,7 @@ static void dm_integrity_io_error(struct dm_integrity_c *ic, const char *msg, in
 
 static int dm_integrity_failed(struct dm_integrity_c *ic)
 {
-	return ACCESS_ONCE(ic->failed);
+	return READ_ONCE(ic->failed);
 }
 
 static commit_id_t dm_integrity_commit_id(struct dm_integrity_c *ic, unsigned i,
@@ -1545,7 +1546,7 @@ retry_kmap:
 		smp_mb();
 		if (unlikely(waitqueue_active(&ic->copy_to_journal_wait)))
 			wake_up(&ic->copy_to_journal_wait);
-		if (ACCESS_ONCE(ic->free_sectors) <= ic->free_sectors_threshold) {
+		if (READ_ONCE(ic->free_sectors) <= ic->free_sectors_threshold) {
 			queue_work(ic->commit_wq, &ic->commit_work);
 		} else {
 			schedule_autocommit(ic);
@@ -1798,7 +1799,7 @@ static void integrity_commit(struct work_struct *w)
 	ic->n_committed_sections += commit_sections;
 	spin_unlock_irq(&ic->endio_wait.lock);
 
-	if (ACCESS_ONCE(ic->free_sectors) <= ic->free_sectors_threshold)
+	if (READ_ONCE(ic->free_sectors) <= ic->free_sectors_threshold)
 		queue_work(ic->writer_wq, &ic->writer_work);
 
 release_flush_bios:
@@ -1980,7 +1981,7 @@ static void integrity_writer(struct work_struct *w)
 	unsigned prev_free_sectors;
 
 	/* the following test is not needed, but it tests the replay code */
-	if (ACCESS_ONCE(ic->suspending))
+	if (READ_ONCE(ic->suspending))
 		return;
 
 	spin_lock_irq(&ic->endio_wait.lock);