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Date: Sat, 17 May 2008 15:45:57 +0200
Message-ID: <s5hwsltm4bu.wl%tiwai@suse.de>
From: Takashi Iwai <tiwai@suse.de>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       bugme-daemon@bugzilla.kernel.org, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Stas Sergeev <stsp@aknet.ru>
Subject: Re: [Bugme-new] [Bug 10701] New: snd_pcsp lockdep warning
In-Reply-To: <alpine.LFD.1.10.0805162132050.3255@apollo.tec.linutronix.de>
References: <bug-10701-10286@http.bugzilla.kernel.org/>
	<20080515110244.6e15d4c3.akpm@linux-foundation.org>
	<alpine.LFD.1.10.0805161338500.3255@apollo.tec.linutronix.de>
	<20080516103827.0d5ab023.akpm@linux-foundation.org>
	<alpine.LFD.1.10.0805162132050.3255@apollo.tec.linutronix.de>
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At Fri, 16 May 2008 21:32:49 +0200 (CEST),
Thomas Gleixner wrote:
> 
> On Fri, 16 May 2008, Andrew Morton wrote:
> > > So the author was well aware of locking problem and the whole code is
> > > just a stupid hack around the problem without solving it. This code is
> > > not at all suited for HRTIMER_CB_IRQSAFE.
> > 
> > You sound impressed!  So what's the fix?  HRTIMER_CB_SOFTIRQ?
> 
> Yeah, impressed by creativity. HRTIMER_CB_SOFTIRQ should be the right
> thing.

Well, it'd be basically a similar way like snd-pcsp currently does ("a
stupid hack" :)  But, it's good to have a fix, anyway, since this
sounds like a generic problem with a callback in a spinlock.  If the
callback requires another own lock, this can easily lead to a AB/BA
deadlock.  Actually, ALSA PCM core had sometimes similar problems,
too.


thanks,

Takashi