linux-kernel - Re: [Bugme-new] [Bug 10701] New: snd

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Date:	Sat, 17 May 2008 15:45:57 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	bugme-daemon@...zilla.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Stas Sergeev <stsp@...et.ru>
Subject: Re: [Bugme-new] [Bug 10701] New: snd_pcsp lockdep warning

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
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