netdev - Re: [PATCH] net: Adjust softirq raising in __napi

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Date:	Wed, 21 Oct 2009 23:39:47 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Tilman Schmidt <tilman@...p.cc>,
	David Miller <davem@...emloft.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,
	Michael Buesch <mb@...sch.de>,
	Oliver Hartkopp <oliver@...tkopp.net>
Subject: Re: [PATCH] net: Adjust softirq raising in __napi_schedule

On Thu, Oct 22, 2009 at 06:25:30AM +0900, Johannes Berg wrote:
> On Wed, 2009-10-21 at 23:19 +0200, Jarek Poplawski wrote:
...
> > --- 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);
> 
> This still doesn't make any sense.
> 
> There may or may not be a lot of code that assumes that everything else
> is run with other tasklets disabled, and that it cannot be interrupted
> by a tasklet and thus create a race.
> 
> Can you prove that is not the case, across the entire networking layer?

I'm not sure I can understand your question. This patch is mainly to
avoid using netif_rx()/netif_rx_ni() pair as a test of proper process
context handling; IMHO there're better tools for this (lockdep,
WARN_ON's).

Jarek P.
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