Re: [PATCH 2/5] rcu: don't check ->donelist in __rcu_pending()

[Srivatsa Vaddagiri]

On Sun, Jan 08, 2006 at 10:19:24PM +0300, Oleg Nesterov wrote:
> ->donelist becomes != NULL only in rcu_process_callbacks().
> 
> rcu_process_callbacks() always calls rcu_do_batch() when
> ->donelist != NULL.
> 
> rcu_do_batch() schedules rcu_process_callbacks() again if
> ->donelist was not flushed entirely.
> 
> So ->donelist != NULL means that rcu_tasklet is either
> TASKLET_STATE_SCHED or TASKLET_STATE_RUN, we don't need to
> check it in __rcu_pending().

Do I smell a bug wrt CPU Hotplug here? Basically, I see that we do
a rcu_move_batch of ->curlist and ->nxtlist of the dead CPU. Why not
->donelist? If we have to do a rcu_move_batch of ->donelist also,
then perhaps the ->donelist != NULL check is required in
rcu_pending? This is considering that the RCU tasklet of the dead
CPU is killed (rather than moved over to a different CPU).


-- 


Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017
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