linux-kernel - [096/140] USB: g_serial: dont set low

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Message-Id: <20100730173111.359649789@clark.site>
Date:	Fri, 30 Jul 2010 10:31:01 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Jon Povey <jon.povey@...elogic.co.uk>,
	Maulik Mankad <x0082077@...com>,
	David Brownell <dbrownell@...rs.sourceforge.net>
Subject: [096/140] USB: g_serial: dont set low_latency flag

2.6.33-stable review patch.  If anyone has any objections, please let us know.

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

From: Jon Povey <jon.povey@...elogic.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@...elogic.co.uk>
Cc: Maulik Mankad <x0082077@...com>
Acked-by: David Brownell <dbrownell@...rs.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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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