See if this one looks sensible. It does leave a tiny race window but that
semes wiser than hacking up the tty kref_put path in the middle of an -rc
series.
Thanks to Daniel and Alan Stern for chasing this down and getting traces. Also
to Daniel for being persistent when I took it as a random odd "only seen by one
user" error which it wasn't.
---
From: Alan Cox <alan@xxxxxxxxxxxxxxx>
The port lock is used to protect the port state. However the port structure
is freed on a hangup, then the lock taken on a close. The right fix is to
drop the port on tty->shutdown() but we can't yet do that due to sleep v
non-sleeping rules. Instead do the next best thing and fix it up when we are
not in -rc season.
Reported-by: Daniel Mack <daniel@xxxxxxxx>
Signed-off-by: Alan Cox <alan@xxxxxxxxxxxxxxx>
---
drivers/usb/serial/usb-serial.c | 19 ++++++++++++++++++-
1 files changed, 18 insertions(+), 1 deletions(-)
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index bd7581b..228d77c 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -340,6 +340,22 @@ static void serial_close(struct tty_struct *tty, struct file *filp)
dbg("%s - port %d", __func__, port->number);
+ /* FIXME:
+ This leaves a very narrow race. Really we should do the
+ serial_do_free() on tty->shutdown(), but tty->shutdown can
+ be called from IRQ context and serial_do_free can sleep.
+
+ The right fix is probably to make the tty free (which is rare)
+ and thus tty->shutdown() occur via a work queue and simplify all
+ the drivers that use it.
+ */
+ if (tty_hung_up_p(filp)) {
+ /* serial_hangup already called serial_down at this point.
+ Another user may have already reopened the port but
+ serial_do_free is refcounted */
+ serial_do_free(port);
+ return;
+ }
if (tty_port_close_start(&port->port, tty, filp) == 0)
return;
@@ -355,7 +371,8 @@ static void serial_hangup(struct tty_struct *tty)
struct usb_serial_port *port = tty->driver_data;
serial_do_down(port);
tty_port_hangup(&port->port);
- serial_do_free(port);
+ /* We must not free port yet - the USB serial layer depends on it's
+ continued existence */
}
static int serial_write(struct tty_struct *tty, const unsigned char *buf,
--
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