[SERIAL] Clean up serial locking when obtaining a reference to a port

The locking for the uart_port is over complicated, and can be
simplified if we introduce a flag to indicate that a port is "dead"
and will be removed.

This also helps the validator because it removes a case of non-nested
unlock ordering.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>

2 files changed, 61 insertions, 54 deletions

diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index fcd7744c4253..aeb8153ccf24 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -1500,20 +1500,18 @@ uart_block_til_ready(struct file *filp, struct uart_state *state)
 static struct uart_state *uart_get(struct uart_driver *drv, int line)
 {
         struct uart_state *state;
+        int ret = 0;
 
-        mutex_lock(&port_mutex);
         state = drv->state + line;
         if (mutex_lock_interruptible(&state->mutex)) {
-                state = ERR_PTR(-ERESTARTSYS);
-                goto out;
+                ret = -ERESTARTSYS;
+                goto err;
         }
 
         state->count++;
-        if (!state->port) {
-                state->count--;
-                mutex_unlock(&state->mutex);
-                state = ERR_PTR(-ENXIO);
-                goto out;
+        if (!state->port || state->port->flags & UPF_DEAD) {
+                ret = -ENXIO;
+                goto err_unlock;
         }
 
         if (!state->info) {
@@ -1531,15 +1529,17 @@ static struct uart_state *uart_get(struct uart_driver *drv, int line)
                         tasklet_init(&state->info->tlet, uart_tasklet_action,
                                      (unsigned long)state);
                 } else {
-                        state->count--;
-                        mutex_unlock(&state->mutex);
-                        state = ERR_PTR(-ENOMEM);
+                        ret = -ENOMEM;
+                        goto err_unlock;
                 }
         }
-
- out:
-        mutex_unlock(&port_mutex);
         return state;
+
+ err_unlock:
+        state->count--;
+        mutex_unlock(&state->mutex);
+ err:
+        return ERR_PTR(ret);
 }
 
 /*
@@ -2085,45 +2085,6 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
         }
 }
 
-/*
- * This reverses the effects of uart_configure_port, hanging up the
- * port before removal.
- */
-static void
-uart_unconfigure_port(struct uart_driver *drv, struct uart_state *state)
-{
-        struct uart_port *port = state->port;
-        struct uart_info *info = state->info;
-
-        if (info && info->tty)
-                tty_vhangup(info->tty);
-
-        mutex_lock(&state->mutex);
-
-        state->info = NULL;
-
-        /*
-         * Free the port IO and memory resources, if any.
-         */
-        if (port->type != PORT_UNKNOWN)
-                port->ops->release_port(port);
-
-        /*
-         * Indicate that there isn't a port here anymore.
-         */
-        port->type = PORT_UNKNOWN;
-
-        /*
-         * Kill the tasklet, and free resources.
-         */
-        if (info) {
-                tasklet_kill(&info->tlet);
-                kfree(info);
-        }
-
-        mutex_unlock(&state->mutex);
-}
-
 static struct tty_operations uart_ops = {
         .open           = uart_open,
         .close          = uart_close,
@@ -2270,6 +2231,7 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
         state = drv->state + port->line;
 
         mutex_lock(&port_mutex);
+        mutex_lock(&state->mutex);
         if (state->port) {
                 ret = -EINVAL;
                 goto out;
@@ -2304,7 +2266,13 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
             port->cons && !(port->cons->flags & CON_ENABLED))
                 register_console(port->cons);
 
+        /*
+         * Ensure UPF_DEAD is not set.
+         */
+        port->flags &= ~UPF_DEAD;
+
  out:
+        mutex_unlock(&state->mutex);
         mutex_unlock(&port_mutex);
 
         return ret;
@@ -2322,6 +2290,7 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
 int uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
 {
         struct uart_state *state = drv->state + port->line;
+        struct uart_info *info;
 
         BUG_ON(in_interrupt());
 
@@ -2332,11 +2301,48 @@ int uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
         mutex_lock(&port_mutex);
 
         /*
+         * Mark the port "dead" - this prevents any opens from
+         * succeeding while we shut down the port.
+         */
+        mutex_lock(&state->mutex);
+        port->flags |= UPF_DEAD;
+        mutex_unlock(&state->mutex);
+
+        /*
          * Remove the devices from devfs
          */
         tty_unregister_device(drv->tty_driver, port->line);
 
-        uart_unconfigure_port(drv, state);
+        info = state->info;
+        if (info && info->tty)
+                tty_vhangup(info->tty);
+
+        /*
+         * All users of this port should now be disconnected from
+         * this driver, and the port shut down.  We should be the
+         * only thread fiddling with this port from now on.
+         */
+        state->info = NULL;
+
+        /*
+         * Free the port IO and memory resources, if any.
+         */
+        if (port->type != PORT_UNKNOWN)
+                port->ops->release_port(port);
+
+        /*
+         * Indicate that there isn't a port here anymore.
+         */
+        port->type = PORT_UNKNOWN;
+
+        /*
+         * Kill the tasklet, and free resources.
+         */
+        if (info) {
+                tasklet_kill(&info->tlet);
+                kfree(info);
+        }
+
         state->port = NULL;
         mutex_unlock(&port_mutex);
 
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index c32e60e79dea..bd14858121ea 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -254,6 +254,7 @@ struct uart_port {
 #define UPF_CONS_FLOW           ((__force upf_t) (1 << 23))
 #define UPF_SHARE_IRQ           ((__force upf_t) (1 << 24))
 #define UPF_BOOT_AUTOCONF       ((__force upf_t) (1 << 28))
+#define UPF_DEAD                ((__force upf_t) (1 << 30))
 #define UPF_IOREMAP             ((__force upf_t) (1 << 31))
 
 #define UPF_CHANGE_MASK         ((__force upf_t) (0x17fff))