On Wed, Oct 02, 2019 at 06:38:57PM -0700, [email protected] wrote: > 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.
So, like Peter said back then, there must be an issue in the scheduler such as a missing or mishandled preemption point. > > [ 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); Just use tick_dep_clear() without for_each_online_cpu(). > 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); Same here. > 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); And here you only need tick_dep_set() without for_each_online_cpu(). Thanks. > return 0; > } > > -- > 2.9.5 >
