Re: [PATCH net 1/3] slip/slcan: added locking in wakeup function

[Peter Hurley]

[ +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

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