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

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Message-Id: <201001191615.47589.oliver@neukum.org>
Date:	Tue, 19 Jan 2010 16:15:47 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
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

Am Dienstag, 19. Januar 2010 15:21:24 schrieb Alan Cox:
> > > > 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.

I don't know which line discipline is used. Matthew?

But anyway, if this can happen buglessly, the generic function
must handle it.

	Regards
		Oliver
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