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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@kernel.org>
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1 changed files with 9 additions and 0 deletions
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@ -2101,6 +2101,9 @@ int rcutree_dead_cpu(unsigned int cpu)
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rcu_boost_kthread_setaffinity(rnp, -1);
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/* Do any needed no-CB deferred wakeups from this CPU. */
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do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu));
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// Stop-machine done, so allow nohz_full to disable tick.
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tick_dep_clear(TICK_DEP_BIT_RCU);
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return 0;
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}
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@ -3085,6 +3088,9 @@ int rcutree_online_cpu(unsigned int cpu)
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return 0; /* Too early in boot for scheduler work. */
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sync_sched_exp_online_cleanup(cpu);
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rcutree_affinity_setting(cpu, -1);
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// Stop-machine done, so allow nohz_full to disable tick.
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tick_dep_clear(TICK_DEP_BIT_RCU);
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return 0;
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}
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@ -3105,6 +3111,9 @@ int rcutree_offline_cpu(unsigned int cpu)
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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rcutree_affinity_setting(cpu, cpu);
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// nohz_full CPUs need the tick for stop-machine to work quickly
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tick_dep_set(TICK_DEP_BIT_RCU);
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return 0;
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}
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