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Re: [PATCH] ipvs:Fix locking requirements in the function ip_vs_unlink_service

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  Re: [PATCH] ipvs:Fix locking requirements in the function  ip_vs_unlink_service Julian Anastasov <ja@ssi.bg> - 2015-09-12 08:30 +0200
    Re: [PATCH] ipvs:Fix locking requirements in the function  ip_vs_unlink_service Julian Anastasov <ja@ssi.bg> - 2015-09-12 20:40 +0200

#1223323 — Re: [PATCH] ipvs:Fix locking requirements in the function ip_vs_unlink_service

	Hello,

On Sat, 12 Sep 2015, Nicholas Krause wrote:

> This fixes locking requirements in the function ip_vs_unlink_service
> to properly use bottom half spinlocking around the call to the function
> __ip_vs_del_service  in order to meet the locking that this paricular
> function requires as stated in it's comments related to locking.

> +	spin_lock_bh(&svc->sched_lock);
>  	__ip_vs_del_service(svc, cleanup);
> +	spin_unlock_bh(&svc->sched_lock);

	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	It seems the comment is outdated after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").

Regards

--
Julian Anastasov <ja@ssi.bg>
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#1223450

	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 	It seems the comment is outdated after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 is outdated.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@ssi.bg>
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