Merge tag 'tty-3.15-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty/serial fixes from Greg KH:
 "Here are some tty and serial driver fixes for things reported
  recently"

* tag 'tty-3.15-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
  tty: Fix lockless tty buffer race
  Revert "tty: Fix race condition between __tty_buffer_request_room and flush_to_ldisc"
  drivers/tty/hvc: don't free hvc_console_setup after init
  n_tty: Fix n_tty_write crash when echoing in raw mode
  tty: serial: 8250_core.c Bug fix for Exar chips.

5 files changed, 20 insertions, 18 deletions

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 94f9e3a38412..0ff7fda0742f 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -190,7 +190,7 @@ static struct tty_driver *hvc_console_device(struct console *c, int *index)
         return hvc_driver;
 }
 
-static int __init hvc_console_setup(struct console *co, char *options)
+static int hvc_console_setup(struct console *co, char *options)
 {       
         if (co->index < 0 || co->index >= MAX_NR_HVC_CONSOLES)
                 return -ENODEV;
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 41fe8a047d37..fe9d129c8735 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2353,8 +2353,12 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
                         if (tty->ops->flush_chars)
                                 tty->ops->flush_chars(tty);
                 } else {
+                        struct n_tty_data *ldata = tty->disc_data;
+
                         while (nr > 0) {
+                                mutex_lock(&ldata->output_lock);
                                 c = tty->ops->write(tty, b, nr);
+                                mutex_unlock(&ldata->output_lock);
                                 if (c < 0) {
                                         retval = c;
                                         goto break_out;
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 0e1bf8858431..2d4bd3929e50 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -555,7 +555,7 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
          */
         if ((p->port.type == PORT_XR17V35X) ||
            (p->port.type == PORT_XR17D15X)) {
-                serial_out(p, UART_EXAR_SLEEP, 0xff);
+                serial_out(p, UART_EXAR_SLEEP, sleep ? 0xff : 0);
                 return;
         }
 
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index f1d30f6945af..cf78d1985cd8 100644
--- 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;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 036cccd80d9f..1c3316a47d7e 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -61,7 +61,6 @@ struct tty_bufhead {
         struct tty_buffer *head;        /* Queue head */
         struct work_struct work;
         struct mutex       lock;
-        spinlock_t         flush_lock;
         atomic_t           priority;
         struct tty_buffer sentinel;
         struct llist_head free;         /* Free queue head */