[PATCH v3 11/45] sched/core: Use get/put_online_cpus_atomic() to prevent CPU offline

[Srivatsa S. Bhat]

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 <mi...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---

 kernel/sched/core.c |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9b1f2e5..9d870bf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1160,11 +1160,11 @@ void kick_process(struct task_struct *p)
 {
        int cpu;
 
-       preempt_disable();
+       get_online_cpus_atomic();
        cpu = task_cpu(p);
        if ((cpu != smp_processor_id()) && task_curr(p))
                smp_send_reschedule(cpu);
-       preempt_enable();
+       put_online_cpus_atomic();
 }
 EXPORT_SYMBOL_GPL(kick_process);
 #endif /* CONFIG_SMP */
@@ -1172,6 +1172,9 @@ EXPORT_SYMBOL_GPL(kick_process);
 #ifdef CONFIG_SMP
 /*
  * ->cpus_allowed is protected by both rq->lock and p->pi_lock
+ *
+ *  Must be called within get/put_online_cpus_atomic(), to prevent
+ *  CPUs from going offline from under us.
  */
 static int select_fallback_rq(int cpu, struct task_struct *p)
 {
@@ -1245,6 +1248,9 @@ out:
 
 /*
  * The caller (fork, wakeup) owns p->pi_lock, ->cpus_allowed is stable.
+ *
+ * Must be called within get/put_online_cpus_atomic(), to prevent
+ * CPUs from going offline from under us.
  */
 static inline
 int select_task_rq(struct task_struct *p, int sd_flags, int wake_flags)
@@ -1489,6 +1495,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, 
int wake_flags)
        unsigned long flags;
        int cpu, success = 0;
 
+       get_online_cpus_atomic();
+
        smp_wmb();
        raw_spin_lock_irqsave(&p->pi_lock, flags);
        if (!(p->state & state))
@@ -1531,6 +1539,7 @@ stat:
 out:
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 
+       put_online_cpus_atomic();
        return success;
 }
 
@@ -1744,6 +1753,8 @@ void wake_up_new_task(struct task_struct *p)
        unsigned long flags;
        struct rq *rq;
 
+       get_online_cpus_atomic();
+
        raw_spin_lock_irqsave(&p->pi_lock, flags);
 #ifdef CONFIG_SMP
        /*
@@ -1766,6 +1777,8 @@ void wake_up_new_task(struct task_struct *p)
                p->sched_class->task_woken(rq, p);
 #endif
        task_rq_unlock(rq, p, &flags);
+
+       put_online_cpus_atomic();
 }
 
 #ifdef CONFIG_PREEMPT_NOTIFIERS
@@ -3879,6 +3892,8 @@ bool __sched yield_to(struct task_struct *p, bool preempt)
        unsigned long flags;
        int yielded = 0;
 
+       get_online_cpus_atomic();
+
        local_irq_save(flags);
        rq = this_rq();
 
@@ -3924,6 +3939,8 @@ out_unlock:
 out_irq:
        local_irq_restore(flags);
 
+       put_online_cpus_atomic();
+
        if (yielded > 0)
                schedule();
 
@@ -4324,9 +4341,11 @@ static int migration_cpu_stop(void *data)
         * The original target cpu might have gone down and we might
         * be on another cpu but it doesn't matter.
         */
+       get_online_cpus_atomic();
        local_irq_disable();
        __migrate_task(arg->task, raw_smp_processor_id(), arg->dest_cpu);
        local_irq_enable();
+       put_online_cpus_atomic();
        return 0;
 }
 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/