Re: [2.6.14-rt1] slowdown / oops.

[Rusty Russell]

On Wed, 2005-11-02 at 16:33 +0100, Ingo Molnar wrote:
> local_bh_disable()/enable() is a NOP under PREEMPT_RT, and the 
> ip_ct_deliver_cached_events PER_CPU code relies on not being preempted 
> by the net_rx_action softirq handler. So this is a bug in PREEMPT_RT and 
> the upstream code should be fine.
> 
> 	Ingo
> 
> Index: linux/net/ipv4/netfilter/ip_conntrack_core.c
> ===================================================================
> --- linux.orig/net/ipv4/netfilter/ip_conntrack_core.c
> +++ linux/net/ipv4/netfilter/ip_conntrack_core.c
> @@ -105,11 +105,11 @@ void ip_ct_deliver_cached_events(const s
>  {
>  	struct ip_conntrack_ecache *ecache;
>  	
> -	local_bh_disable();
> +	read_lock_bh(&ip_conntrack_lock);
>  	ecache = &__get_cpu_var(ip_conntrack_ecache);
>  	if (ecache->ct == ct)
>  		__ip_ct_deliver_cached_events(ecache);
> -	local_bh_enable();
> +	read_unlock_bh(&ip_conntrack_lock);

This kind of change is troubling.  I suppose we could go to per-cpu
locks, but it's still a loss.

Rusty.
-- 
A bad analogy is like a leaky screwdriver -- Richard Braakman

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