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

From: Florian Westphal
Date: Sat Jan 09 2016 - 20:07:25 EST

Sasha Levin <sasha.levin@xxxxxxxxxx> 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.

Reviewed-by: Florian Westphal <fw@xxxxxxxxx>