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 <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-19-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

fs/userfaultfd.c

@@ -381,7 +381,7 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	 * in __get_user_pages if userfaultfd_release waits on the
 	 * caller of handle_userfault to release the mmap_sem.
 	 */
-	if (unlikely(ACCESS_ONCE(ctx->released))) {
+	if (unlikely(READ_ONCE(ctx->released))) {
 		/*
 		 * Don't return VM_FAULT_SIGBUS in this case, so a non
 		 * cooperative manager can close the uffd after the
@@ -477,7 +477,7 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason)
 						       vmf->flags, reason);
 	up_read(&mm->mmap_sem);
 
-	if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
+	if (likely(must_wait && !READ_ONCE(ctx->released) &&
 		   (return_to_userland ? !signal_pending(current) :
 		    !fatal_signal_pending(current)))) {
 		wake_up_poll(&ctx->fd_wqh, POLLIN);
@@ -586,7 +586,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 		set_current_state(TASK_KILLABLE);
 		if (ewq->msg.event == 0)
 			break;
-		if (ACCESS_ONCE(ctx->released) ||
+		if (READ_ONCE(ctx->released) ||
 		    fatal_signal_pending(current)) {
 			/*
 			 * &ewq->wq may be queued in fork_event, but
@@ -833,7 +833,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 	struct userfaultfd_wake_range range = { .len = 0, };
 	unsigned long new_flags;
 
-	ACCESS_ONCE(ctx->released) = true;
+	WRITE_ONCE(ctx->released, true);
 
 	if (!mmget_not_zero(mm))
 		goto wakeup;