Merge branch 'merge' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc

[karo-tx-linux.git] / drivers / tty / tty_buffer.c

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index f1d30f6945af2cf8fece1a5a1b40d59aa46cd5e0..cf78d1985cd851fb2b6615054bfabf5a8e3b2b13 100644 (file)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -255,16 +255,15 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size,
        if (change || left < size) {
                /* This is the slow path - looking for new buffers to use */
                if ((n = tty_buffer_alloc(port, size)) != NULL) {
-                       unsigned long iflags;
-
                        n->flags = flags;
                        buf->tail = n;
-
-                       spin_lock_irqsave(&buf->flush_lock, iflags);
                        b->commit = b->used;
+                       /* 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;
-                       spin_unlock_irqrestore(&buf->flush_lock, iflags);
-
                } else if (change)
                        size = 0;
                else
@@ -448,27 +447,28 @@ static void flush_to_ldisc(struct work_struct *work)
        mutex_lock(&buf->lock);
 
        while (1) {
-               unsigned long flags;
                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;
 
-               spin_lock_irqsave(&buf->flush_lock, flags);
+               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) {
-                               spin_unlock_irqrestore(&buf->flush_lock, flags);
+                       if (next == NULL)
                                break;
-                       }
-                       buf->head = head->next;
-                       spin_unlock_irqrestore(&buf->flush_lock, flags);
+                       buf->head = next;
                        tty_buffer_free(port, head);
                        continue;
                }
-               spin_unlock_irqrestore(&buf->flush_lock, flags);
 
                count = receive_buf(tty, head, count);
                if (!count)
@@ -523,7 +523,6 @@ void tty_buffer_init(struct tty_port *port)
        struct tty_bufhead *buf = &port->buf;
 
        mutex_init(&buf->lock);
-       spin_lock_init(&buf->flush_lock);
        tty_buffer_reset(&buf->sentinel, 0);
        buf->head = &buf->sentinel;
        buf->tail = &buf->sentinel;