netdev - Re: [rfc] IPVS: convert scheduler management to RCU

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Date:	Fri, 20 Aug 2010 13:54:11 -0400
From:	yao zhao <dragonlinux@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>, Simon Horman <horms@...ge.net.au>,
	lvs-devel@...r.kernel.org, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org,
	Stephen Hemminger <shemminger@...tta.com>,
	Wensong Zhang <wensong@...ux-vs.org>,
	Julian Anastasov <ja@....bg>,
	Paul E McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [rfc] IPVS: convert scheduler management to RCU

On Fri, Aug 20, 2010 at 11:32 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le vendredi 20 août 2010 à 11:04 -0400, yao zhao a écrit :
>
>> The code here is deleting a global from the list, am I right? I didn't
>> see any called case.
>> what are you going to do more? free it? write_unlock_bh should make the mb.
>
>
> If you dont wait _after_ delete from list and following actions
> (kfree() without a call_rcu(), or module unload, or whatever), a reader
> might access your data/code and crash the box.
>
> spin_unlock_bh() wont help you at all, since only writers are freezed by
> the lock (since readers only hold rcu_lock)
>
> Documentation/RCU/whatisRCU.txt line 705
>
> Documentation/RCU/checklist.txt  15)
>
>
>
>
I read the code again and that global is in a module then you are right.
If that global is not in a module then you don't need it at all, as in
that global only functions pointer or name... which never be changed.

yao
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