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>

8 files changed, 11 insertions, 11 deletions

diff --git a/kernel/acct.c b/kernel/acct.c
index 5e72af29ab73..21eedd0dd81a 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -146,7 +146,7 @@ static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)
 again:
 	smp_rmb();
 	rcu_read_lock();
-	res = to_acct(ACCESS_ONCE(ns->bacct));
+	res = to_acct(READ_ONCE(ns->bacct));
 	if (!res) {
 		rcu_read_unlock();
 		return NULL;
@@ -158,7 +158,7 @@ again:
 	}
 	rcu_read_unlock();
 	mutex_lock(&res->lock);
-	if (res != to_acct(ACCESS_ONCE(ns->bacct))) {
+	if (res != to_acct(READ_ONCE(ns->bacct))) {
 		mutex_unlock(&res->lock);
 		acct_put(res);
 		goto again;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 824a583079a1..8fd2f2d1358a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1200,7 +1200,7 @@ perf_event_ctx_lock_nested(struct perf_event *event, int nesting)
 
 again:
 	rcu_read_lock();
-	ctx = ACCESS_ONCE(event->ctx);
+	ctx = READ_ONCE(event->ctx);
 	if (!atomic_inc_not_zero(&ctx->refcount)) {
 		rcu_read_unlock();
 		goto again;
@@ -5302,8 +5302,8 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 		if (!rb)
 			goto aux_unlock;
 
-		aux_offset = ACCESS_ONCE(rb->user_page->aux_offset);
-		aux_size = ACCESS_ONCE(rb->user_page->aux_size);
+		aux_offset = READ_ONCE(rb->user_page->aux_offset);
+		aux_size = READ_ONCE(rb->user_page->aux_size);
 
 		if (aux_offset < perf_data_size(rb) + PAGE_SIZE)
 			goto aux_unlock;
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index f684d8e5fa2b..f3e37971c842 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -381,7 +381,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
 	 * (B) <-> (C) ordering is still observed by the pmu driver.
 	 */
 	if (!rb->aux_overwrite) {
-		aux_tail = ACCESS_ONCE(rb->user_page->aux_tail);
+		aux_tail = READ_ONCE(rb->user_page->aux_tail);
 		handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
 		if (aux_head - aux_tail < perf_aux_size(rb))
 			handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb));
diff --git a/kernel/exit.c b/kernel/exit.c
index f6cad39f35df..6b4298a41167 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1339,7 +1339,7 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
 	 * Ensure that EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE transition
 	 * can't confuse the checks below.
 	 */
-	int exit_state = ACCESS_ONCE(p->exit_state);
+	int exit_state = READ_ONCE(p->exit_state);
 	int ret;
 
 	if (unlikely(exit_state == EXIT_DEAD))
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 81279c6602ff..845f3805c73d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2724,7 +2724,7 @@ rb_reserve_next_event(struct ring_buffer *buffer,
 	 * if it happened, we have to fail the write.
 	 */
 	barrier();
-	if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
+	if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
 		local_dec(&cpu_buffer->committing);
 		local_dec(&cpu_buffer->commits);
 		return NULL;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 652c682707cd..9050c8b3ccde 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1459,7 +1459,7 @@ extern struct trace_event_file *find_event_file(struct trace_array *tr,
 
 static inline void *event_file_data(struct file *filp)
 {
-	return ACCESS_ONCE(file_inode(filp)->i_private);
+	return READ_ONCE(file_inode(filp)->i_private);
 }
 
 extern struct mutex event_mutex;
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 49cb41412eec..780262210c9a 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -77,7 +77,7 @@ check_stack(unsigned long ip, unsigned long *stack)
 {
 	unsigned long this_size, flags; unsigned long *p, *top, *start;
 	static int tracer_frame;
-	int frame_size = ACCESS_ONCE(tracer_frame);
+	int frame_size = READ_ONCE(tracer_frame);
 	int i, x;
 
 	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index c490f1e4313b..d32b45662fb6 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -894,7 +894,7 @@ static bool new_idmap_permitted(const struct file *file,
 int proc_setgroups_show(struct seq_file *seq, void *v)
 {
 	struct user_namespace *ns = seq->private;
-	unsigned long userns_flags = ACCESS_ONCE(ns->flags);
+	unsigned long userns_flags = READ_ONCE(ns->flags);
 
 	seq_printf(seq, "%s\n",
 		   (userns_flags & USERNS_SETGROUPS_ALLOWED) ?