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

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Message-Id: <200910032035.21884.mb@bu3sch.de>
Date:	Sat, 3 Oct 2009 20:35:19 +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 Saturday 03 October 2009 20:26:22 Michael Buesch wrote:
> On Saturday 03 October 2009 14:06:57 Tilman Schmidt wrote:
> > Move calls to handle_minor_send() and handle_minor_recv() out of
> > the sections locked by workaround_lock.
> > - handle_minor_send() may call another CAPI function via the card
> >   driver, deadlocking by trying to take workaround_lock again.
> > - handle_minor_recv() calls the receive_buf method of the active
> >   line discipline which may sleep.
> 
> I remember that handle_minor_send() and/or handle_minor_recv() showed up
> in the crash backtraces. So if you move them out of the critical
> section, you can as well remove the lock completely.
> 

here's my original mail:
http://lkml.indiana.edu/hypermail/linux/kernel/0605.0/0455.html

Note the patch in that mail does _not_ fix the issue, as it turned out later.
Then I did the workaround-lock patch, which _did_ fix it.

But in that mail you can see the original crash backtraces, which might be
useful for finding out what _really_ happened.

-- 
Greetings, Michael.
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