@@ -3338,7 +3338,8 @@ done:
*
* Returns the target CPU number, or the same CPU if no balancing is needed.
*
- * preempt must be disabled.
+ * Must be called within get/put_online_cpus_atomic(), to prevent CPUs
+ * from going offline from under us.
*/
static int
select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
@@ -5267,6 +5268,8 @@ void idle_balance(int this_cpu, struct rq *this_rq)
raw_spin_unlock(&this_rq->lock);
update_blocked_averages(this_cpu);
+
+ get_online_cpus_atomic();
rcu_read_lock();
for_each_domain(this_cpu, sd) {
unsigned long interval;
@@ -5290,6 +5293,7 @@ void idle_balance(int this_cpu, struct rq *this_rq)
}
}
rcu_read_unlock();
+ put_online_cpus_atomic();
raw_spin_lock(&this_rq->lock);
@@ -5316,6 +5320,7 @@ static int active_load_balance_cpu_stop(void *data)
struct rq *target_rq = cpu_rq(target_cpu);
struct sched_domain *sd;
+ get_online_cpus_atomic();
raw_spin_lock_irq(&busiest_rq->lock);
/* make sure the requested cpu hasn't gone down in the meantime */
@@ -5367,6 +5372,7 @@ static int active_load_balance_cpu_stop(void *data)
out_unlock:
busiest_rq->active_balance = 0;
raw_spin_unlock_irq(&busiest_rq->lock);
+ put_online_cpus_atomic();
return 0;
}
@@ -5527,6 +5533,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
update_blocked_averages(cpu);
+ get_online_cpus_atomic();
rcu_read_lock();
for_each_domain(cpu, sd) {
if (!(sd->flags & SD_LOAD_BALANCE))
@@ -5575,6 +5582,7 @@ out:
break;
}
rcu_read_unlock();
+ put_online_cpus_atomic();
/*
* next_balance will be updated only when there is a need.
@@ -5706,6 +5714,7 @@ static void run_rebalance_domains(struct softirq_action *h)
enum cpu_idle_type idle = this_rq->idle_balance ?
CPU_IDLE : CPU_NOT_IDLE;
+ get_online_cpus_atomic();
rebalance_domains(this_cpu, idle);
/*
@@ -5714,6 +5723,7 @@ static void run_rebalance_domains(struct softirq_action *h)
* stopped.
*/
nohz_idle_balance(this_cpu, idle);
+ put_online_cpus_atomic();
}
static inline int on_null_domain(int cpu)
@@ -5731,8 +5741,10 @@ void trigger_load_balance(struct rq *rq, int cpu)
likely(!on_null_domain(cpu)))
raise_softirq(SCHED_SOFTIRQ);
#ifdef CONFIG_NO_HZ_COMMON
+ get_online_cpus_atomic();
if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
nohz_balancer_kick(cpu);
+ put_online_cpus_atomic();
#endif
}
Once stop_machine() is gone from the CPU offline path, we won't be able to depend on disabling preemption to prevent CPUs from going offline from under us. Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline, while invoking from atomic context. Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> --- kernel/sched/fair.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)