linux-kernel - Re: [REGRESSION] "USB: use kfifo to buffer usb-generic serial writes" causes gobi

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Message-ID: <20100119142124.6f2a7034@lxorguk.ukuu.org.uk>
Date:	Tue, 19 Jan 2010 14:21:24 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>, dvomlehn@...co.com,
	gregkh@...e.de, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [REGRESSION] "USB: use kfifo to buffer usb-generic serial
 writes" causes gobi_loader to hang

On Tue, 19 Jan 2010 14:57:00 +0100
Oliver Neukum <oliver@...kum.org> wrote:

> Am Dienstag, 19. Januar 2010 14:29:34 schrieb Alan Cox:
> > On Tue, 19 Jan 2010 14:20:29 +0100
> > Oliver Neukum <oliver@...kum.org> wrote:
> > 
> > > Am Montag, 18. Januar 2010 21:14:16 schrieb Matthew Garrett:
> > > 
> > > > drivers/usb/serial/generic.c: usb_serial_generic_write - port 0, 1565 
> > > > bytes
> > > > drivers/usb/serial/generic.c: usb_serial_generic_write - put 0 bytes 
> > > > into fifo
> > > > drivers/usb/serial/generic.c: usb_serial_generic_read_bulk_callback - 
> > > > port 0
> > > 
> > > If the FIFO is full we can do nothing. Please try the attached patch.
> > 
> > If the FIFO is full how are we getting called - we should have throttled
> > earlier if there is any flow control (including 'look no URBs' cases) ?
> 
> The log shows no call to usb_serial_generic_write_room()
> Do you consider this a bug in the tty layer?

Some of the line disciplines just throw data at the board but not n_tty
(the normal one) - so for PPP you wouldn't see checks on room but the
loader I assume is using the normal tty layer - if so something is up
because the ldisc shouldn't have written more than there is room for.
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