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SubjectRe: TTY loosing data with u_serial gadget
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,
flush_to_ldisc, receive_room to small count=225, receive_room=1031,
flush_to_ldisc, receive_room to small count=33, receive_room=4095,

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
> list know if you still have problems with it?
> thanks,
> greg k-h

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