On Thu, Aug 30, 2012 at 11:56:18AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul.mcken...@linaro.org> > > The rcu_preempt_offline_tasks() moves all tasks queued on a given leaf > rcu_node structure to the root rcu_node, which is done when the last CPU > corresponding the the leaf rcu_node structure goes offline. Now that > RCU-preempt's synchronize_rcu_expedited() implementation blocks CPU-hotplug > operations during the initialization of each rcu_node structure's > ->boost_tasks pointer, rcu_preempt_offline_tasks() can do a better job > of setting the root rcu_node's ->boost_tasks pointer. > > The key point is that rcu_preempt_offline_tasks() runs as part of the > CPU-hotplug process, so that a concurrent synchronize_rcu_expedited() is > guaranteed to either have not started on the one hand (in which case there > is no boosting on behalf of the expedited grace period) to be completely
Missing word: s/to be/or to be/ > initialized on the other (in which case, in absence of other priority s/absence/the absence/ > boosting, all ->boost_tasks pointers will be initialized). Therefore, > if rcu_preempt_offline_tasks() finds that the ->boost_tasks pointer is > equal to the ->exp_tasks pointer, it can be sure that it is correcty > placed. > > The case where there was boosting ongoing at the time that the s/The/In the/ > synchronize_rcu_expedited() function started, different nodes might > start boosting the tasks blocking the expedited grace period at different > times. In this mixed case, the root node will either be boosting tasks > for the expedited grace period already, or it will start as soon as it > gets done boosting for the normal grace period -- but in this latter > case, the root node's tasks needed to be boosted in any case. > > This commit therefore adds a check of the ->boost_tasks pointer against > the ->exp_tasks pointer to the list that prevents updating ->boost_tasks. Seems like some hint of this explanation really ought to end up in a comment somewhere... > Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <j...@joshtriplett.org> > --- > kernel/rcutree_plugin.h | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index b1b4851..c930a47 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -591,7 +591,8 @@ static int rcu_preempt_offline_tasks(struct rcu_state > *rsp, > /* In case root is being boosted and leaf was not. */ > raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ > if (rnp_root->boost_tasks != NULL && > - rnp_root->boost_tasks != rnp_root->gp_tasks) > + rnp_root->boost_tasks != rnp_root->gp_tasks && > + rnp_root->boost_tasks != rnp_root->exp_tasks) > rnp_root->boost_tasks = rnp_root->gp_tasks; > raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ > #endif /* #ifdef CONFIG_RCU_BOOST */ > -- > 1.7.8 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
