[RFC PATCH v2 08/10] yield_to(),cpu-hotplug: Prevent offlining of other CPUs properly

From: Srivatsa S. Bhat
Date: Wed Dec 05 2012 - 13:45:50 EST


Once stop_machine() is gone from the CPU offline path, we won't be able to
depend on local_irq_save() to prevent CPUs from going offline from under us.

Use the get/put_online_cpus_atomic_light() APIs to prevent changes to the
cpu_online_mask, while invoking from atomic context.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

kernel/sched/core.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 84a8579..1ef595a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4312,6 +4312,7 @@ bool __sched yield_to(struct task_struct *p, bool preempt)
unsigned long flags;
bool yielded = 0;

+ get_online_cpus_atomic_light();
local_irq_save(flags);
rq = this_rq();

@@ -4339,13 +4340,14 @@ again:
* Make p's CPU reschedule; pick_next_entity takes care of
* fairness.
*/
- if (preempt && rq != p_rq)
+ if (preempt && rq != p_rq && cpu_online(task_cpu(p)))
resched_task(p_rq->curr);
}

out:
double_rq_unlock(rq, p_rq);
local_irq_restore(flags);
+ put_online_cpus_atomic_light();

if (yielded)
schedule();

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