linux-kernel - Re: NOHZ: local_softirq

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Message-ID: <4AD31213.6020006@imap.cc>
Date:	Mon, 12 Oct 2009 13:25:07 +0200
From:	Tilman Schmidt <tilman@...p.cc>
To:	David Miller <davem@...emloft.net>
CC:	tilman@...p.cc, johannes@...solutions.net,
	hidave.darkstar@...il.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linux-wireless@...r.kernel.org,
	linux-ppp@...r.kernel.org, netdev@...r.kernel.org, paulus@...ba.org
Subject: Re: NOHZ: local_softirq_pending 08

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On Mon, 12 Oct 2009 03:32:46 -0700 (PDT), David Miller wrote:
> The PPP receive paths in ppp_generic.c do a local_bh_disable()/
> local_bh_enable() around packet receiving (via ppp_recv_lock()/
> ppp_recv_unlock() in ppp_do_recv).
> 
> So at least that part is perfectly fine.
> 
> ppp_input(), as called from ppp_sync_process(), also disables BH's
> around ppp_do_recv() calls (via read_lock_bh()/read_unlock_bh()).
> 
> So that's fine too.
> 
> Do you have a bug report or are you just scanning around looking
> for trouble? :-)

I have encountered the message in the subject during a test of
the Gigaset CAPI driver, and would like to determine whether
it's a bug in the driver, a bug somewhere else, or no bug at
all. The test scenario was PPP over ISDN with pppd+capiplugin.
In an alternative scenario, also PPP over ISDN but with
smpppd+capidrv, the message did not occur.

Johannes' answer pointed me to the netif_rx() function.
The Gigaset driver itself doesn't call that function at all.
In the scenario where I saw the message, it was the SYNC_PPP
line discipline that did. But from your explanation I gather
that the cause cannot lie there.

So now I'm looking for other possible causes of that message.

- --
Tilman Schmidt                    E-Mail: tilman@...p.cc
Bonn, Germany
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