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Date: Mon, 09 Jan 2006 18:33:03 +0300
From: Oleg Nesterov <oleg@tv-sign.ru>
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To: vatsa@in.ibm.com
Cc: linux-kernel@vger.kernel.org, Dipankar Sarma <dipankar@in.ibm.com>,
       Manfred Spraul <manfred@colorfullife.com>,
       Linus Torvalds <torvalds@osdl.org>,
       "Paul E. McKenney" <paulmck@us.ibm.com>, Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH 2/5] rcu: don't check ->donelist in __rcu_pending()
References: <43C165BC.F7C6DCF5@tv-sign.ru> <20060109093141.GA10811@in.ibm.com> <43C2785C.4E937748@tv-sign.ru> <20060109134238.GA26700@in.ibm.com>
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Srivatsa Vaddagiri wrote:
> 
> On Mon, Jan 09, 2006 at 05:51:08PM +0300, Oleg Nesterov wrote:
> > Srivatsa Vaddagiri wrote:
> > >             If we have to do a rcu_move_batch of ->donelist also,
> > > then perhaps the ->donelist != NULL check is required in
> > > rcu_pending?
> >
> > rcu_move_batch() always adds entries to the ->nxttail, so I think
> > this patch is correct.
> 
> Hmm ..adding entries on dead cpu's ->donelist to ->nxtlist of some other CPU
> doesnt make sense (it re-triggers graceperiods for all those callbacks which is
> not needed).

Yes, but this is rare event, so ...

>              Maybe rcu_move_batch should take that into account and instead add
> to ->donelist of current CPU which is processing the CPU_DEAD callback.

May be you are right,

> In which case, ->donelist != NULL check is still reqd in rcu_pending ?

Yes, in that case it is required. Do you think it is worth to optimize
CPU_DEAD case?

Oleg.