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

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Message-ID: <87lhw7inzg.fsf@nemi.mork.no>
Date:	Tue, 18 Mar 2014 15:24:19 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Miller <davem@...emloft.net>, stephen@...workplumber.org,
	eric.dumazet@...il.com, 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.

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.


Bjørn
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