From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757502AbZGFJ7X (ORCPT ); Mon, 6 Jul 2009 05:59:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752554AbZGFJ7P (ORCPT ); Mon, 6 Jul 2009 05:59:15 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:44521 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751404AbZGFJ7O (ORCPT ); Mon, 6 Jul 2009 05:59:14 -0400 Date: Mon, 6 Jul 2009 11:00:14 +0100 From: Alan Cox To: Herbert Xu Cc: Michael Guntsche , linux-kernel@vger.kernel.org Subject: Re: BUG: scheduling while atomic Message-ID: <20090706110014.5cbcc2d7@lxorguk.ukuu.org.uk> In-Reply-To: <20090706074333.GA17276@gondor.apana.org.au> References: <23AED400-6DA5-462F-94F0-BEE34AC08A7A@it-loops.com> <20090627140643.7140f6a9@lxorguk.ukuu.org.uk> <33C7D336-F062-47B3-9033-D3DC465F793C@it-loops.com> <20090706074333.GA17276@gondor.apana.org.au> X-Mailer: Claws Mail 3.7.1 (GTK+ 2.14.7; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > So what see here is that on xmit from the network, > PPP will call pty_write from BH context which eventually leads > to tty_throttle and the sleep. That would I fit the symptoms and also explain why some broken versions of the USB code on embedded devices also exploded with PPP over USB links. Not however at all easy to fix as it only ever worked in the past on the "close both eyes, pray and jump" principle of locking. Added to the todo list for later this week. The pty layer has all sorts of magic hackery to allow it to call back and forth without going via internal tty buffering like normal hardware. That may have to die as it causes other horrible problems too. Alan