The following commit has been merged into the core/rcu branch of tip: Commit-ID: 96926686deab853bcacf887501f4ed958e38666b Gitweb: https://git.kernel.org/tip/96926686deab853bcacf887501f4ed958e38666b Author: Paul E. McKenney <paulmck@xxxxxxxxxx> AuthorDate: Fri, 02 Aug 2019 15:12:47 -07:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Sat, 05 Oct 2019 10:46:05 -07:00 rcu: Make CPU-hotplug removal operations enable tick CPU-hotplug removal operations run the multi_cpu_stop() function, which relies on the scheduler to gain control from whatever is running on the various online CPUs, including any nohz_full CPUs running long loops in kernel-mode code. Lack of the scheduler-clock interrupt on such CPUs can delay multi_cpu_stop() for several minutes and can also result in RCU CPU stall warnings. This commit therefore causes CPU-hotplug removal operations to enable the scheduler-clock interrupt on all online CPUs. [ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ] [ paulmck: Apply simplifications suggested by Frederic Weisbecker. ] Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/tree.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a5c296d..7c67ea5 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2101,6 +2101,9 @@ int rcutree_dead_cpu(unsigned int cpu) rcu_boost_kthread_setaffinity(rnp, -1); /* Do any needed no-CB deferred wakeups from this CPU. */ do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu)); + + // Stop-machine done, so allow nohz_full to disable tick. + tick_dep_clear(TICK_DEP_BIT_RCU); return 0; } @@ -3085,6 +3088,9 @@ int rcutree_online_cpu(unsigned int cpu) return 0; /* Too early in boot for scheduler work. */ sync_sched_exp_online_cleanup(cpu); rcutree_affinity_setting(cpu, -1); + + // Stop-machine done, so allow nohz_full to disable tick. + tick_dep_clear(TICK_DEP_BIT_RCU); return 0; } @@ -3105,6 +3111,9 @@ int rcutree_offline_cpu(unsigned int cpu) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); rcutree_affinity_setting(cpu, cpu); + + // nohz_full CPUs need the tick for stop-machine to work quickly + tick_dep_set(TICK_DEP_BIT_RCU); return 0; }
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