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From: Greg KH on 30 Jul 2010 13:50
2.6.33-stable review patch. If anyone has any objections, please let us know.

------------------

From: Jon Povey <jon.povey(a)racelogic.co.uk>

commit 44a0c0190b500ee6bcfc0976fe540f65dee2cd67 upstream.

No longer set low_latency flag as it causes this warning backtrace:

WARNING: at kernel/mutex.c:207 __mutex_lock_slowpath+0x6c/0x288()

Fix associated locking and wakeups.

Signed-off-by: Jon Povey <jon.povey(a)racelogic.co.uk>
Cc: Maulik Mankad <x0082077(a)ti.com>
Acked-by: David Brownell <dbrownell(a)users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
drivers/usb/gadget/u_serial.c | 15 ++-------------
1 file changed, 2 insertions(+), 13 deletions(-)

--- a/drivers/usb/gadget/u_serial.c
+++ b/drivers/usb/gadget/u_serial.c
@@ -535,17 +535,11 @@ recycle:
list_move(&req->list, &port->read_pool);
}

- /* Push from tty to ldisc; this is immediate with low_latency, and
- * may trigger callbacks to this driver ... so drop the spinlock.
+ /* Push from tty to ldisc; without low_latency set this is handled by
+ * a workqueue, so we won't get callbacks and can hold port_lock
*/
if (tty && do_push) {
- spin_unlock_irq(&port->port_lock);
tty_flip_buffer_push(tty);
- wake_up_interruptible(&tty->read_wait);
- spin_lock_irq(&port->port_lock);
-
- /* tty may have been closed */
- tty = port->port_tty;
}


@@ -783,11 +777,6 @@ static int gs_open(struct tty_struct *tt
port->open_count = 1;
port->openclose = false;

- /* low_latency means ldiscs work in tasklet context, without
- * needing a workqueue schedule ... easier to keep up.
- */
- tty->low_latency = 1;
-
/* if connected, start the I/O stream */
if (port->port_usb) {
struct gserial *gser = port->port_usb;


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