netdev - Re: [PATCH 6/6] net: Free skbs from irqs when possible.

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Date:	Tue, 18 Mar 2014 08:23:49 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Miller <davem@...emloft.net>, stephen@...workplumber.org,
	netdev@...r.kernel.org, xiyou.wangcong@...il.com, mpm@...enic.com,
	satyam.sharma@...il.com
Subject: Re: [PATCH 6/6] net: Free skbs from irqs when possible.

On Tue, 2014-03-18 at 15:24 +0100, Bjørn Mork wrote:
> Ben Hutchings <ben@...adent.org.uk> writes:
> > On Mon, 2014-03-17 at 23:27 -0700, Eric W. Biederman wrote:
> > [...]
> >> --- a/net/core/skbuff.c
> >> +++ b/net/core/skbuff.c
> >> @@ -554,14 +554,21 @@ static void kfree_skbmem(struct sk_buff *skb)
> >>  
> >>  static void skb_release_head_state(struct sk_buff *skb)
> >>  {
> >> +	WARN_ONCE(in_irq() && !skb_irq_freeable(skb),
> >> +		  "%s called from irq! sp %d nfct %d frag_list %d %pF dst %lx",
> >> +		  __func__,
> >> +		  IS_ENABLED(CONFIG_XFRM) ? !!skb->sp : 0,
> >> +		  IS_ENABLED(CONFIG_NF_CONNTRACK) ? !!skb->nfct : 0,
> > [...]
> >
> > This is a syntax error if CONFIG_XFRM or CONFIG_NF_CONNTRACK is
> > disabled; you have to use #ifdef's.
> 
> Are you sure?  I thought one of the ideas behind these macros was that
> they would always evaluate to 0 or 1.  The docs says:
> 
>  * IS_ENABLED(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y' or 'm',
>  * 0 otherwise.
> 
> 
> See include/linux/kconfig.h for the macro magic making this
> happen. Looks like fun figuring that out.

It has nothing to do with this.

Try following code, and you'll get a compilation error.

unsigned int can_this_fly(struct sk_buff *skb)
{
	return IS_ENABLED(CONFIG_NOWAY_SIR) ? skb->unknown_field : 0;
}


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