From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH net 1/3] slip/slcan: added locking in wakeup function Date: Thu, 19 Sep 2013 06:43:16 -0400 Message-ID: <523AD544.7030100@hurleysoftware.com> References: <1379093833-4949-1-git-send-email-nautsch2@gmail.com> <1379093833-4949-2-git-send-email-nautsch2@gmail.com> <523AC589.5040006@pengutronix.de> <523AD21C.8030102@gmail.com> <523AD356.70607@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Andre Naujoks , davem@davemloft.net, Wolfgang Grandegger , linux-can@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Greg KH To: Marc Kleine-Budde Return-path: In-Reply-To: <523AD356.70607@pengutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org [ +cc Greg Kroah-Hartman] On 09/19/2013 06:35 AM, Marc Kleine-Budde wrote: > On 09/19/2013 12:29 PM, Andre Naujoks wrote: >> On 19.09.2013 11:36, schrieb Marc Kleine-Budde: >>> On 09/13/2013 07:37 PM, Andre Naujoks wrote: >>>> The locking is needed, since the the internal buffer for the CAN >>>> frames is changed during the wakeup call. This could cause buffer >>>> inconsistencies under high loads, especially for the outgoing >>>> short CAN packet skbuffs. >>>> >>>> The needed locks led to deadlocks before commit >>>> "5ede52538ee2b2202d9dff5b06c33bfde421e6e4 tty: Remove extra >>>> wakeup from pty write() path", which removed the direct callback >>>> to the wakeup function from the tty layer. >>> >>> What does that mean for older kernels? (< >>> 5ede52538ee2b2202d9dff5b06c33bfde421e6e4) >> >> It seems the slcan (and slip) driver is broken for older kernels. See >> this thread for a discussion about the patch in pty.c. >> >> http://marc.info/?l=linux-kernel&m=137269017002789&w=2 > > Thanks for the info. > >> The patch from Peter Hurley was actually already in the queue, when I >> ran into the problem, and is now in kernel 3.12. >> >> Without the pty patch and slow CAN traffic, the driver works, because >> the wakeup is called directly from the pty driver. That is also the >> reason why there was no locking. It would just deadlock. >> >> When the pty driver defers the wakeup, we ran into synchronisation >> problems (which should be fixed by the locking) and eventually into a >> kernel panic because of a recursive loop (which should be fixed by the >> pty.c patch). >> >> Maybe it is possible to get both patches back into the stable branches? > > Sounds reasonable. You might get in touch with Peter Hurley, if his > patch is scheduled for stable. Documentation/stable_kernel_rules.txt > suggests a procedure if your patch depends on others to be cherry picked. Already following along. I'd like to wait for 3.12 release before the pty patch goes to -stable (so that it gets more in-the-wild testing). Regards, Peter Hurley