netdev - Re: [PATCH] genetlink: make netns aware

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Date:	Fri, 19 Jun 2009 03:12:10 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Netdev <netdev@...r.kernel.org>
Cc:	Thomas Graf <tgraf@...g.ch>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH] genetlink: make netns aware

On Thu, 2009-06-18 at 13:17 +0200, Johannes Berg wrote:
> This makes generic netlink network namespace aware.

Please drop this patch, it has a deadlock bug.

> +int genlmsg_multicast(struct sk_buff *skb, u32 pid,
> +		      unsigned int group, gfp_t flags)
> +{
> +	int ret;
> +
> +	if (flags & GFP_ATOMIC) {
> +		rcu_read_lock();
> +		ret = genlmsg_mcast(skb, pid, group, flags);
> +		rcu_read_unlock();
> +	} else {
> +		rtnl_lock();
> +		ret = genlmsg_mcast(skb, pid, group, flags);
> +		rtnl_unlock();
> +	}
> +
> +	return ret;
> +}

It used to be possible to call genlmsg_multicast() under rtnl, which
will now obviously deadlock unless you also make it GFP_ATOMIC... I'm
inclined to always use RCU here to solve that, comments?

johannes

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