[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>
diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index fcd7744..aeb8153 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -1500,20 +1500,18 @@
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 @@
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 @@
}
}
-/*
- * 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 @@
state = drv->state + port->line;
mutex_lock(&port_mutex);
+ mutex_lock(&state->mutex);
if (state->port) {
ret = -EINVAL;
goto out;
@@ -2304,7 +2266,13 @@
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_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 @@
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);