Merge branches 'for-3.16/i2c-hid', 'for-3.16/rmi4', 'for-3.16/sony' and 'for-3.16...

[firefly-linux-kernel-4.4.55.git] / drivers / tty / tty_buffer.c

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 8ebd9f88a6f69ff85f63139944fad2542c789483..cf78d1985cd851fb2b6615054bfabf5a8e3b2b13 100644 (file)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -258,7 +258,11 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size,
                        n->flags = flags;
                        buf->tail = n;
                        b->commit = b->used;
-                       smp_mb();
+                       /* paired w/ barrier 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;
                } else if (change)
                        size = 0;
@@ -444,17 +448,24 @@ static void flush_to_ldisc(struct work_struct *work)
 
        while (1) {
                struct tty_buffer *head = buf->head;
+               struct tty_buffer *next;
                int count;
 
                /* Ldisc or user is trying to gain exclusive access */
                if (atomic_read(&buf->priority))
                        break;
 
+               next = head->next;
+               /* paired w/ barrier in __tty_buffer_request_room();
+                * ensures commit value read is not stale if the head
+                * is advancing to the next buffer
+                */
+               smp_rmb();
                count = head->commit - head->read;
                if (!count) {
-                       if (head->next == NULL)
+                       if (next == NULL)
                                break;
-                       buf->head = head->next;
+                       buf->head = next;
                        tty_buffer_free(port, head);
                        continue;
                }