On Sun, Jan 08, 2006 at 10:19:24PM +0300, Oleg Nesterov wrote:
> ->donelist becomes != NULL only in rcu_process_callbacks().
>
> 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().
>
> [ This patch was tested with rcutorture.ko, I don't understand
> it's output, but it says "End of test: SUCCESS". So if this
> patch incorrect blame Paul, not me! ]
>
> Signed-off-by: Oleg Nesterov <[email protected]>
>
> --- 2.6.15/kernel/rcupdate.c~2_DONE 2006-01-08 21:35:21.000000000 +0300
> +++ 2.6.15/kernel/rcupdate.c 2006-01-08 21:55:45.000000000 +0300
> @@ -454,10 +454,6 @@ static int __rcu_pending(struct rcu_ctrl
> if (!rdp->curlist && rdp->nxtlist)
> return 1;
>
> - /* This cpu has finished callbacks to invoke */
> - if (rdp->donelist)
> - return 1;
> -
> /* The rcu core waits for a quiescent state from the cpu */
> if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
> return 1;
This may not be a good idea. For example, during cpu hotplug,
a cpu may inherit a set of finished callbacks that need to be
invoked. So, an rcu_pending() check needs to detect that.
Thanks
Dipankar
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