rcu: Make CPU-hotplug removal operations enable tick (96926686) · Commits · 戴 / test

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@kernel.org>

kernel/rcu/tree.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

Admin message