linux-kernel - Re: [PATCH] ipvs:Fix locking requirements in the function ip_vs_unlink

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Message-ID: <alpine.LFD.2.11.1509122111110.1491@ja.home.ssi.bg>
Date:	Sat, 12 Sep 2015 21:28:36 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	nick <xerofoify@...il.com>
cc:	wensong@...ux-vs.org, horms@...ge.net.au, pablo@...filter.org,
	kaber@...sh.net, kadlec@...ckhole.kfki.hu, davem@...emloft.net,
	netdev@...r.kernel.org, lvs-devel@...r.kernel.org,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipvs:Fix locking requirements in the function
 ip_vs_unlink_service


	Hello,

On Sat, 12 Sep 2015, nick wrote:

> > 	BH locking is not needed anymore. Also, sched_lock is
> > used by schedulers to protect only access to svc->sched_data
> > fields.
> > 
> > 	It seems the comment is outdated after
> > commit ceec4c381681 ("ipvs: convert services to rcu").
> > 
> Julian,
> You are correct after reading the commit id for rcu locking conversion that this comment
> is outdated. However the locking may still be required but in terms of rcu_read_lock/
> unlock around this function call as it's still a critical region.

	This function is called under __ip_vs_mutex, so
there is single writer that modifies the configuration.
As "readers" the schedulers access the configuration under
rcu_read_lock (eg. called in tcp_conn_schedule) but they
are free to use other locking too. ip_vs_wlc.c scheduler
is example where sched_lock is not used because only
svc->destinations is accessed which is protected with RCU
by definition. You can check __ip_vs_unlink_dest() how
dest is unlinked with list_del_rcu() before sched->del_dest
method is called.

Regards

--
Julian Anastasov <ja@....bg>
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