locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()

Please do not apply this to mainline directly, instead please re-run the
coccinelle script shown below and apply its output.

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 harmful, and changing them results in
churn.

However, for some features, the read/write distinction is critical to
correct operation. To distinguish these cases, separate read/write
accessors must be used. This patch migrates (most) remaining
ACCESS_ONCE() instances to {READ,WRITE}_ONCE(), using the following
coccinelle script:

----
// Convert trivial ACCESS_ONCE() uses to equivalent READ_ONCE() and
// WRITE_ONCE()

// $ make coccicheck COCCI=/home/mark/once.cocci SPFLAGS="--include-headers" MODE=patch

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 <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

fs/namei.c

@@ -1209,7 +1209,7 @@ static int follow_managed(struct path *path, struct nameidata *nd)
 	/* Given that we're not holding a lock here, we retain the value in a
 	 * local variable for each dentry as we look at it so that we don't see
 	 * the components of that value change under us */
-	while (managed = ACCESS_ONCE(path->dentry->d_flags),
+	while (managed = READ_ONCE(path->dentry->d_flags),
 	       managed &= DCACHE_MANAGED_DENTRY,
 	       unlikely(managed != 0)) {
 		/* Allow the filesystem to manage the transit without i_mutex
@@ -1394,7 +1394,7 @@ int follow_down(struct path *path)
 	unsigned managed;
 	int ret;
 
-	while (managed = ACCESS_ONCE(path->dentry->d_flags),
+	while (managed = READ_ONCE(path->dentry->d_flags),
 	       unlikely(managed & DCACHE_MANAGED_DENTRY)) {
 		/* Allow the filesystem to manage the transit without i_mutex
 		 * being held.