tty: Replace smp_rmb/smp_wmb with smp_load_acquire/smp_store_release

Clarify flip buffer producer/consumer operation; the use of
smp_load_acquire() and smp_store_release() more clearly indicates
which memory access requires a barrier.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 4cf263d..25ba5af 100644 (file)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -291,12 +291,11 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size,
                        n->flags = flags;
                        buf->tail = n;
                        b->commit = b->used;
-                       /* paired w/ barrier in flush_to_ldisc(); ensures the
+                       /* paired w/ acquire in flush_to_ldisc(); ensures the
                         * latest commit value can be read before the head is
                         * advanced to the next buffer
                         */
-                       smp_wmb();
-                       b->next = n;
+                       smp_store_release(&b->next, n);
                } else if (change)
                        size = 0;
                else
@@ -488,12 +487,11 @@ static void flush_to_ldisc(struct work_struct *work)
                if (atomic_read(&buf->priority))
                        break;
 
-               next = head->next;
-               /* paired w/ barrier in __tty_buffer_request_room();
+               /* paired w/ release in __tty_buffer_request_room();
                 * ensures commit value read is not stale if the head
                 * is advancing to the next buffer
                 */
-               smp_rmb();
+               next = smp_load_acquire(&head->next);
                count = head->commit - head->read;
                if (!count) {
                        if (next == NULL) {