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Date: Sat, 15 Jun 2013 16:12:22 +0800 From: Cong Wang <amwang@...hat.com> To: Eric Dumazet <eric.dumazet@...il.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 00:55 -0700, Eric Dumazet wrote: > 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 ? I really missed this in your previous reply, sorry. I assume you mean ip_mc_inc_group(in_dev, addr), yes. > > 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. I _did_ try to replace spinlock with mutex, but apparently mutex_lock() can't be called with rcu_read_lock() held, which is the case in ip_mc_drop_socket(). BTW, if you think this is a problem, IPv6 has the same problem, since it uses rwlock. Thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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