linux-kernel - Re: NOHZ: local_softirq

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Message-ID: <20091015114052.GA9870@ff.dom.local>
Date:	Thu, 15 Oct 2009 11:40:52 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Tilman Schmidt <tilman@...p.cc>
Cc:	David Miller <davem@...emloft.net>, 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

On 12-10-2009 13:25, Tilman Schmidt wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> 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.

Anyway, I agree with Michael Buesch there is no reason to waste time
for tracking all netif_rx vs netif_rx_ni uses, and it seems we could
avoid it by using the "proper" version of raise_softirq_irqoff() in
__napi_schedule(). Could anybody try if I'm not wrong?

Thanks,
Jarek P.
---

 net/core/dev.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 28b0b9e..7fc4009 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2728,7 +2728,7 @@ void __napi_schedule(struct napi_struct *n)
 
 	local_irq_save(flags);
 	list_add_tail(&n->poll_list, &__get_cpu_var(softnet_data).poll_list);
-	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
+	raise_softirq_irqoff(NET_RX_SOFTIRQ);
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL(__napi_schedule);
--
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