linux-kernel - Re: NOHZ: local_softirq

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Message-Id: <200910111217.31883.mb@bu3sch.de>
Date:	Sun, 11 Oct 2009 12:17:30 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Dave Young <hidave.darkstar@...il.com>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: NOHZ: local_softirq_pending 08

On Sunday 11 October 2009 12:08:55 Johannes Berg wrote:
> On Sun, 2009-10-11 at 17:52 +0800, Dave Young wrote:
> 
> > With kernel 2.6.32-rc3-00052-g0eca52a I got following KERN_ERR
> > messages just while using firefox:
> > 
> > [  130.527399] NOHZ: local_softirq_pending 08
> 
> > Any idea? or known issue?
> 
> Are you using b43 (or wl12x1)? If so, it's a known issue, but the driver
> was recently left without an active maintainer in a brouhaha about a bug
> fix.
> 
> Cf. http://thread.gmane.org/gmane.linux.kernel.wireless.general/39440
> 
> Absent proof that mac80211 is safe to run with BHs enabled, the correct
> solution is disabling tasklets around the RX function, unlike all the
> proposed patches. However, Michael thinks it's such a bad solution that
> he has refused to implement it.

Ehm, no. That's not exactly true.
We call the non-_irqsafe functions, which by definition are designed to
run in non-irq (soft or hard) context. At least that's how I understand the
documentation, last time I read it.
Why don't you simply do local_bh_disable() in those functions, if they
require bh disabled, instead of depending on the driver doing it?

> FWIW, I believe the bug to be in b43 and wl12x1, and not as Michael
> thinks in the stack.

If mac80211 requires BHs disabled, it should do this.

-- 
Greetings, Michael.
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