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authorAlan Stern <stern@rowland.harvard.edu>2009-09-01 11:38:59 -0400
committerLive-CD User <linux@linux.site>2009-09-19 13:13:40 -0700
commit8bc2c1b2daf95029658868cb1427baea2da87139 (patch)
tree9895248e23de85d55a4d4ec9234aec7e58de285b
parentf5b0953a89fa3407fb293cc54ead7d8feec489e4 (diff)
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: Alan Stern <stern@rowland.harvard.edu> Cc: stable <stable@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--drivers/usb/serial/usb-serial.c31
1 files changed, 23 insertions, 8 deletions
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 266dc583867..87802ea8bbc 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -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)
- kref_get(&serial->kref);
+ 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->type->init_termios)
- serial->type->init_termios(tty);
- usb_serial_put(serial);
+ 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;
}