netdev - Re: [Patch net-next v5 3/3] igmp: convert RTNL lock to a spinlock

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Message-ID: <1371282946.3252.148.camel@edumazet-glaptop>
Date:	Sat, 15 Jun 2013 00:55:46 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <amwang@...hat.com>
Cc:	netdev@...r.kernel.org,
	Stephen Hemminger <stephen@...workplumber.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [Patch net-next v5 3/3] igmp: convert RTNL lock to a spinlock

On Sat, 2013-06-15 at 15:41 +0800, Cong Wang wrote:
> From: Cong Wang <amwang@...hat.com>
> 
> It is not necessary to hold RTNL lock to protect mc_list,
> at least IPv6 mcast is using a local spinlock, IPv4 can do
> this too. This patch converts RTNL lock+RCU to spinlock+RCU.
> 
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Stephen Hemminger <stephen@...workplumber.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Signed-off-by: Cong Wang <amwang@...hat.com>
> ---
> v5: no change
> v4: rebased on the latest net-next.
> v3: remove useless synchronize_rcu().

Really I think this patch is not needed and way too risky.

I already said that you added bugs, and you keep posting same bugs ?

ip_mc_join_group() seems buggy after your v5 patch ?

Let me repeat : fast path already uses RCU.

The writer parts are slow path, using a mutex is much better than a
spinlock as a mutex allows the writer to use GFP_KERNEL allocations, and
eventually be preempted/scheduled.

Just leave this code as is, this is a waste of time.



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