USB: g_serial: don't set low_latency flag

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@racelogic.co.uk>
Cc: Maulik Mankad <x0082077@ti.com>
Cc: stable <stable@kernel.org>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/gadget/u_serial.c b/drivers/usb/gadget/u_serial.c
index 16bdf77..a0f79df 100644 (file)
--- a/drivers/usb/gadget/u_serial.c
+++ b/drivers/usb/gadget/u_serial.c
@@ -536,17 +536,11 @@ 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;
        }
 
 
@@ -784,11 +778,6 @@ static int gs_open(struct tty_struct *tty, struct file *file)
        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;