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Commit 68ac64cd authored by Russell King's avatar Russell King Committed by Russell King
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[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: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
parent e0a515bc

drivers/serial/serial_core.c

+60 −54
Original line number Diff line number Diff line
@@ -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());
@@ -2331,12 +2300,49 @@ 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);

include/linux/serial_core.h

+1 −0
Original line number Diff line number Diff line
@@ -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))