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	Thu, 14 Oct 2004 16:34:38 -0400
Subject: Re: [patch] Real-Time Preemption, -VP-2.6.9-rc4-mm1-U1
From: Daniel Walker <dwalker@mvista.com>
Reply-To: dwalker@mvista.com
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org
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This fixed it..


Daniel


On Thu, 2004-10-14 at 12:57, Ingo Molnar wrote:
> * Daniel Walker <dwalker@mvista.com> wrote:
> 
> > This was during NFS startup in init.
> > 
> > using smp_processor_id() in preemptible [00000001] code:
> > rpc.rquotad/2158
> > caller is ipt_do_table+0x7b/0x3a0
> >  [<c011aa15>] smp_processor_id+0x95/0xa0
> >  [<c038cbfb>] ipt_do_table+0x7b/0x3a0
> 
> ugh, this is a nasty one - if you look at the TABLE_OFFSET trickery in
> ipt_do_table it's basically an open-coded per-CPU variable in essence. 
> (probably predating percpu.h so it's fair.) Could you try the quick hack
> below? (it compiles but is otherwise untested)
> 
> The proper solution would be to change the code to use per-cpu variables
> (and get that patch accepted upstream) and then trivially convert it to
> get_cpu_var_locked().
> 
> 	Ingo
> 
> --- linux/net/ipv4/netfilter/ip_tables.c.orig
> +++ linux/net/ipv4/netfilter/ip_tables.c
> @@ -287,10 +287,14 @@ ipt_do_table(struct sk_buff **pskb,
>  	 * match it. */
>  	offset = ntohs(ip->frag_off) & IP_OFFSET;
>  
> +#ifdef CONFIG_PREEMPT_REALTIME
> +	write_lock_bh(&table->lock);
> +#else
>  	read_lock_bh(&table->lock);
> +#endif
>  	IP_NF_ASSERT(table->valid_hooks & (1 << hook));
>  	table_base = (void *)table->private->entries
> -		+ TABLE_OFFSET(table->private, smp_processor_id());
> +		+ TABLE_OFFSET(table->private, _smp_processor_id());
>  	e = get_entry(table_base, table->private->hook_entry[hook]);
>  
>  #ifdef CONFIG_NETFILTER_DEBUG
> @@ -397,7 +401,11 @@ ipt_do_table(struct sk_buff **pskb,
>  #ifdef CONFIG_NETFILTER_DEBUG
>  	((struct ipt_entry *)table_base)->comefrom = 0xdead57ac;
>  #endif
> +#ifdef CONFIG_PREEMPT_REALTIME
> +	write_unlock_bh(&table->lock);
> +#else
>  	read_unlock_bh(&table->lock);
> +#endif
>  
>  #ifdef DEBUG_ALLOW_ALL
>  	return NF_ACCEPT;

-
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