locking/barriers: Convert users of lockless_dereference() to READ_ONCE()

[ Note, this is a Git cherry-pick of the following commit:

    506458efaf15 ("locking/barriers: Convert users of lockless_dereference() to READ_ONCE()")

  ... for easier x86 PTI code testing and back-porting. ]

READ_ONCE() now has an implicit smp_read_barrier_depends() call, so it
can be used instead of lockless_dereference() without any change in
semantics.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1508840570-22169-4-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 10 insertions, 10 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 11f273d2f018..3f88c9d32f7e 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -366,7 +366,7 @@ static struct pgpath *choose_path_in_pg(struct multipath *m,
 
 	pgpath = path_to_pgpath(path);
 
-	if (unlikely(lockless_dereference(m->current_pg) != pg)) {
+	if (unlikely(READ_ONCE(m->current_pg) != pg)) {
 		/* Only update current_pgpath if pg changed */
 		spin_lock_irqsave(&m->lock, flags);
 		m->current_pgpath = pgpath;
@@ -390,7 +390,7 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
 	}
 
 	/* Were we instructed to switch PG? */
-	if (lockless_dereference(m->next_pg)) {
+	if (READ_ONCE(m->next_pg)) {
 		spin_lock_irqsave(&m->lock, flags);
 		pg = m->next_pg;
 		if (!pg) {
@@ -406,7 +406,7 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
 
 	/* Don't change PG until it has no remaining paths */
 check_current_pg:
-	pg = lockless_dereference(m->current_pg);
+	pg = READ_ONCE(m->current_pg);
 	if (pg) {
 		pgpath = choose_path_in_pg(m, pg, nr_bytes);
 		if (!IS_ERR_OR_NULL(pgpath))
@@ -473,7 +473,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
 	struct request *clone;
 
 	/* Do we need to select a new pgpath? */
-	pgpath = lockless_dereference(m->current_pgpath);
+	pgpath = READ_ONCE(m->current_pgpath);
 	if (!pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))
 		pgpath = choose_pgpath(m, nr_bytes);
 
@@ -535,7 +535,7 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m
 	bool queue_io;
 
 	/* Do we need to select a new pgpath? */
-	pgpath = lockless_dereference(m->current_pgpath);
+	pgpath = READ_ONCE(m->current_pgpath);
 	queue_io = test_bit(MPATHF_QUEUE_IO, &m->flags);
 	if (!pgpath || !queue_io)
 		pgpath = choose_pgpath(m, nr_bytes);
@@ -1804,7 +1804,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
 	struct pgpath *current_pgpath;
 	int r;
 
-	current_pgpath = lockless_dereference(m->current_pgpath);
+	current_pgpath = READ_ONCE(m->current_pgpath);
 	if (!current_pgpath)
 		current_pgpath = choose_pgpath(m, 0);
 
@@ -1826,7 +1826,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
 	}
 
 	if (r == -ENOTCONN) {
-		if (!lockless_dereference(m->current_pg)) {
+		if (!READ_ONCE(m->current_pg)) {
 			/* Path status changed, redo selection */
 			(void) choose_pgpath(m, 0);
 		}
@@ -1895,9 +1895,9 @@ static int multipath_busy(struct dm_target *ti)
 		return (m->queue_mode != DM_TYPE_MQ_REQUEST_BASED);
 
 	/* Guess which priority_group will be used at next mapping time */
-	pg = lockless_dereference(m->current_pg);
-	next_pg = lockless_dereference(m->next_pg);
-	if (unlikely(!lockless_dereference(m->current_pgpath) && next_pg))
+	pg = READ_ONCE(m->current_pg);
+	next_pg = READ_ONCE(m->next_pg);
+	if (unlikely(!READ_ONCE(m->current_pgpath) && next_pg))
 		pg = next_pg;
 
 	if (!pg) {