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Commit 8bc2c1b2 authored by Alan Stern's avatar Alan Stern Committed by Live-CD User
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usb-serial: change logic of serial lookups 



This patch (as1286) changes usb_serial_get_by_index().  Now the
routine will check whether the serial device has been disconnected; if
it has then the return value will be NULL.  If the device hasn't been
disconnected then the routine will return with serial->disc_mutex
held, so that the caller can use the structure without fear of racing
against driver unloads.

This permits the scope of table_mutex in destroy_serial() to be
reduced.  Instead of protecting the entire function, it suffices to
protect the part that actually uses serial_table[], i.e., the call to
return_serial().  There's no longer any danger of the refcount being
incremented after it reaches 0 (which was the reason for having the
large scope previously), because it can't reach 0 until the serial
device has been disconnected.

Also, the patch makes serial_install() check that serial is non-NULL
before attempting to use it.

Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent f5b0953a

drivers/usb/serial/usb-serial.c

+23 −8
Original line number Diff line number Diff line
@@ -66,6 +66,11 @@ static struct usb_serial *serial_table[SERIAL_TTY_MINORS]; 
static DEFINE_MUTEX(table_lock);

static LIST_HEAD(usb_serial_driver_list);



/*

 * Look up the serial structure.  If it is found and it hasn't been

 * disconnected, return with its disc_mutex held and its refcount

 * incremented.  Otherwise return NULL.

 */

struct usb_serial *usb_serial_get_by_index(unsigned index)

{

	struct usb_serial *serial;
@@ -73,8 +78,15 @@ struct usb_serial *usb_serial_get_by_index(unsigned index) 
	mutex_lock(&table_lock);

	serial = serial_table[index];



	if (serial)

	if (serial) {

		mutex_lock(&serial->disc_mutex);

		if (serial->disconnected) {

			mutex_unlock(&serial->disc_mutex);

			serial = NULL;

		} else {

			kref_get(&serial->kref);

		}

	}

	mutex_unlock(&table_lock);

	return serial;

}
@@ -123,8 +135,10 @@ static void return_serial(struct usb_serial *serial) 


	dbg("%s", __func__);



	mutex_lock(&table_lock);

	for (i = 0; i < serial->num_ports; ++i)

		serial_table[serial->minor + i] = NULL;

	mutex_unlock(&table_lock);

}



static void destroy_serial(struct kref *kref)
@@ -158,9 +172,7 @@ static void destroy_serial(struct kref *kref) 


void usb_serial_put(struct usb_serial *serial)

{

	mutex_lock(&table_lock);

	kref_put(&serial->kref, destroy_serial);

	mutex_unlock(&table_lock);

}



/*****************************************************************************
@@ -190,9 +202,12 @@ static int serial_install(struct tty_driver *driver, struct tty_struct *tty) 
			return retval;

		/* allow the driver to update it */

		serial = usb_serial_get_by_index(tty->index);

		if (serial) {

			if (serial->type->init_termios)

				serial->type->init_termios(tty);

			usb_serial_put(serial);

			mutex_unlock(&serial->disc_mutex);

		}

	}

	/* Final install (we use the default method) */

	tty_driver_kref_get(driver);
@@ -218,7 +233,6 @@ static int serial_open (struct tty_struct *tty, struct file *filp) 
		return -ENODEV;

	}



	mutex_lock(&serial->disc_mutex);

	portNumber = tty->index - serial->minor;

	port = serial->port[portNumber];

	if (!port || serial->disconnected)
@@ -529,6 +543,7 @@ static int serial_proc_show(struct seq_file *m, void *v) 


		seq_putc(m, '\n');

		usb_serial_put(serial);

		mutex_unlock(&serial->disc_mutex);

	}

	return 0;

}