netdev - Re: [PATCH] netfilter: nf_conntrack: use safer way to lock all buckets

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Date:	Sun, 10 Jan 2016 02:06:37 +0100
From:	Florian Westphal <fw@...len.de>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	pablo@...filter.org, kaber@...sh.net, kadlec@...ckhole.kfki.hu,
	davem@...emloft.net, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netfilter: nf_conntrack: use safer way to lock all
 buckets

Sasha Levin <sasha.levin@...cle.com> wrote:
> When we need to lock all buckets in the connection hashtable we'd attempt to
> lock 1024 spinlocks, which is way more preemption levels than supported by
> the kernel.

You're right.

> Fix this by using a global lock and synchronize all buckets on it when we
> need to lock them all. This is pretty heavyweight, but is only done when we
> need to resize the hashtable, and that doesn't happen often enough (or at all).

> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> index 3cb3cb8..3c008ce 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -66,6 +66,32 @@ EXPORT_SYMBOL_GPL(nf_conntrack_locks);
>  __cacheline_aligned_in_smp DEFINE_SPINLOCK(nf_conntrack_expect_lock);
>  EXPORT_SYMBOL_GPL(nf_conntrack_expect_lock);
>  
> +spinlock_t nf_conntrack_locks_all_lock;
> +bool nf_conntrack_locks_all;

Seems both of these can be static and __read_mostly too --
as you already note resizing virtually never happens.

Otherwise:
Reviewed-by: Florian Westphal <fw@...len.de>