From: "Paul E. McKenney" <[email protected]> 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. ] Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f708d54..74bf5c65 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2091,6 +2091,7 @@ static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) */ int rcutree_dead_cpu(unsigned int cpu) { + int c; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ @@ -2101,6 +2102,10 @@ 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. + for_each_online_cpu(c) + tick_dep_clear_cpu(c, TICK_DEP_BIT_RCU); return 0; } @@ -3074,6 +3079,7 @@ static void rcutree_affinity_setting(unsigned int cpu, int outgoing) */ int rcutree_online_cpu(unsigned int cpu) { + int c; unsigned long flags; struct rcu_data *rdp; struct rcu_node *rnp; @@ -3087,6 +3093,10 @@ 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. + for_each_online_cpu(c) + tick_dep_clear_cpu(c, TICK_DEP_BIT_RCU); return 0; } @@ -3096,6 +3106,7 @@ int rcutree_online_cpu(unsigned int cpu) */ int rcutree_offline_cpu(unsigned int cpu) { + int c; unsigned long flags; struct rcu_data *rdp; struct rcu_node *rnp; @@ -3107,6 +3118,10 @@ 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 + for_each_online_cpu(c) + tick_dep_set_cpu(c, TICK_DEP_BIT_RCU); return 0; } -- 2.9.5
