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

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Date:	Fri, 20 Aug 2010 17:32:17 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	yao zhao <dragonlinux@...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

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)



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