linux-kernel - Re: [PATCH RFC] isdn/capi: fix up CAPI subsystem workaround locking a bit

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Message-Id: <200910062301.24572.mb@bu3sch.de>
Date:	Tue, 6 Oct 2009 23:01:22 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Tilman Schmidt <tilman@...p.cc>
Cc:	i4ldeveloper@...tserv.isdn4linux.de,
	Carsten Paeth <calle@...le.de>,
	Karsten Keil <isdn@...ux-pingi.de>,
	Karsten Keil <keil@...systems.de>,
	Armin Schindler <armin@...ware.de>,
	isdn4linux@...tserv.isdn4linux.de, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] isdn/capi: fix up CAPI subsystem workaround locking a bit

On Tuesday 06 October 2009 19:52:55 Tilman Schmidt wrote:
> > Yeah, this sledgehammer lock did fix the crash while leaving the old non-list-head
> > queue in place (it should still be there today).
> 
> That is not the case. In mainline, your second patch was applied on
> top of the first one, so there is now struct list_head ackqueue and
> spinlock_t ackqlock as well as static DEFINE_SPINLOCK(workaround_lock).

Ok, that's fine, too.
It's just that the ackqlock wasn't enough to fix it, as I said. It just shrinks the window.

> > I still have the device somewhere. If you want to have it, I can blow off the
> > dust and send it to you. If you don't want it, I'll throw it away soon.
> > I'd really like to send it to you to get rid of it. ;)
> 
> Feel free to do so. I'll send you my snailmail address by PM. I'm
> making no promises about when I might get around to actually testing
> it, though.

Thanks, I'll get it to the post office by the end of the week.

> >> Can anyone shed some light on 
> >> what that device is doing differently from other ISDN cards?
> > 
> > Well, it's a combined ISDN/DSL card, but I never used the ISDN part. So the crash
> > happened while transferring data over the DSL link.
> 
> DSL over CAPI? Strange.

Yeah, dunno. They did it that way... Pretty weird.

> > The vendor driver is closed source with an open wrapper (like nvidia). It's a pretty
> > crappy unmaintained piece of software, but it ran stable with some patches applied
> > to the driver and the workaround-lock patch to the capi stack.
> 
> O dear. I wonder what I'll find.

ftp://ftp.avm.de/cardware/fritzcrd.dsl/linux/suse.93/fcdsl-suse93-3.11-07.tar.gz

This is the driver that I used. It needs some modification to compile on a recent kernel.
Unfortunately I don't have the patch anymore. But it was rather trivial. It renamed some functions,
because they clashed with others and did some other things I don't remember.
Remember to get a bucket before looking at the code, because you will need it. ;)

-- 
Greetings, Michael.
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