Re: TTY loosing data with u_serial gadget

From: Stefan Bigler
Date: Fri Mar 18 2011 - 12:55:06 EST

Hi Greg

Thanks for your quick answer. Meanwhile we ported our board to 2.6.38.
We recognize the same problem again.
I had also a look at the relevant fixes, a lot is done but I could not find
the required protection of the attribute receive_room.

I added a printk in case of failure were receive_room shows more
space that is really available in the queue and also used.

The printk is attached below and also the log.


flush_to_ldisc, receive_room to small count=201, receive_room=287, real_room=0
flush_to_ldisc, receive_room to small count=225, receive_room=1031, real_room=0
flush_to_ldisc, receive_room to small count=33, receive_room=4095, real_room=0

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index d8210ca..fa9ca62 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -442,6 +442,21 @@ static void flush_to_ldisc(struct work_struct *work)
line discipline as we want to empty the queue */
if (test_bit(TTY_FLUSHPENDING, &tty->flags))
+ /* add printk in case of inconsistante size */
+ if (tty->raw) {
+ unsigned long flags_r;
+ int real_room;
+ spin_lock_irqsave(&tty->read_lock, flags_r);
+ real_room = N_TTY_BUF_SIZE -tty->read_cnt - 1;
+ if (real_room < min(count, tty->receive_room)) {
+ printk(KERN_ERR "flush_to_ldisc, receive_room to small count=%d,"
+ " receive_room=%d, real_room=%d\n",
+ count, tty->receive_room, real_room);
+ }
+ spin_unlock_irqrestore(&tty->read_lock, flags_r);
+ }
if (!tty->receive_room || seen_tail) {
schedule_delayed_work(&tty->, 1);

Am 03/17/2011 01:04 AM, wrote Greg KH:
On Wed, Mar 16, 2011 at 09:47:50PM +0100, Stefan Bigler wrote:
Hi all

I'm facing a problem with TTY loosing data using u_serial gadget.

I have a MPC8247 based system running 2.6.33.
Oh, that's an old kernel, lots of work on the tty layer has happened
since then that would fix issues like this.

If you are stuck using this kernel, please go ask your vendor for
support for it.

If not, can you try out 2.6.38 and let us, and the
linux-usb@xxxxxxxxxxxxxxx list know if you still have problems with it?


greg k-h

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