linux-kernel - Re: [PATCH] USB: ftdi_sio: Remove tty->low

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Date:	Fri, 2 Oct 2009 10:47:55 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Johan Hovold <jhovold@...il.com>,
	Michael Trimarchi <trimarchi@...dalf.sssup.it>,
	Oliver Neukum <oliver@...kum.org>, linux-usb@...r.kernel.org,
	Alan Cox <alan@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: ftdi_sio: Remove tty->low_latency.

On Thu, Oct 01, 2009 at 07:52:21PM -0700, Eric W. Biederman wrote:
> Alan Cox <alan@...rguk.ukuu.org.uk> writes:
> 
> >> As it stands today ftdi_sio does indeed call tty_flip_buffer_push from
> >> interrupt context with low_latency set and that is obviously incorrect,
> >> right?
> >
> > It seems to do it from a work queue - or did I miss a case ?
> 
> ftdi_sio crash quite regularly for me with 2.6.31.
> 
> With a bunch of nasties like:
> BUG: scheduling while atomic: swapper/0/0x00010000
> bad: scheduling from the idle thread!

It's the same problem.

Greg, can't we apply the patch for stable at least? Then we can massage
ftdi_sio into actually using the work queue for doing _all_ processing
in the meantime if deemed necessary.

Alan, did you have time to look at it? Are there any reasons for wanting
to keep low_latency in ftdi_sio when it was removed from all other
drivers processing in interrupt context (without doing work queue
re-implementations)?

Thanks,
Johan

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