linux-kernel - [RFC PATCH v3 7/9] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly

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Message-ID: <20121207173950.27305.39499.stgit@srivatsabhat.in.ibm.com>
Date:	Fri, 07 Dec 2012 23:09:53 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	tglx@...utronix.de, peterz@...radead.org,
	paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	vincent.guittot@...aro.org, tj@...nel.org, oleg@...hat.com
Cc:	sbw@....edu, amit.kucheria@...aro.org, rostedt@...dmis.org,
	rjw@...k.pl, srivatsa.bhat@...ux.vnet.ibm.com,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v3 7/9] yield_to(),
 cpu-hotplug: Prevent offlining of other CPUs properly

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() APIs to prevent CPUs from going offline,
while invoking from atomic context.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 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 cff7656..4b982bf 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();
 	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();
 
 	if (yielded)
 		schedule();

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