[PATCH v2 14/45] sched/rt: Use get/put_online_cpus_atomic() toprevent CPU offline

From: Srivatsa S. Bhat
Date: Tue Jun 25 2013 - 16:31:21 EST


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@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

kernel/sched/rt.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 01970c8..03d9f38 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -6,6 +6,7 @@
#include "sched.h"

#include <linux/slab.h>
+#include <linux/cpu.h>

int sched_rr_timeslice = RR_TIMESLICE;

@@ -28,7 +29,9 @@ static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
if (!overrun)
break;

+ get_online_cpus_atomic();
idle = do_sched_rt_period_timer(rt_b, overrun);
+ put_online_cpus_atomic();
}

return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
@@ -547,6 +550,7 @@ static int do_balance_runtime(struct rt_rq *rt_rq)
int i, weight, more = 0;
u64 rt_period;

+ get_online_cpus_atomic();
weight = cpumask_weight(rd->span);

raw_spin_lock(&rt_b->rt_runtime_lock);
@@ -588,6 +592,7 @@ next:
raw_spin_unlock(&iter->rt_runtime_lock);
}
raw_spin_unlock(&rt_b->rt_runtime_lock);
+ put_online_cpus_atomic();

return more;
}
@@ -1168,6 +1173,10 @@ static void yield_task_rt(struct rq *rq)
#ifdef CONFIG_SMP
static int find_lowest_rq(struct task_struct *task);

+/*
+ * Must be called within get/put_online_cpus_atomic(), to prevent CPUs
+ * from going offline from under us.
+ */
static int
select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
{
@@ -1561,6 +1570,8 @@ retry:
return 0;
}

+ get_online_cpus_atomic();
+
/* We might release rq lock */
get_task_struct(next_task);

@@ -1611,6 +1622,7 @@ retry:
out:
put_task_struct(next_task);

+ put_online_cpus_atomic();
return ret;
}

@@ -1630,6 +1642,7 @@ static int pull_rt_task(struct rq *this_rq)
if (likely(!rt_overloaded(this_rq)))
return 0;

+ get_online_cpus_atomic();
for_each_cpu(cpu, this_rq->rd->rto_mask) {
if (this_cpu == cpu)
continue;
@@ -1695,6 +1708,7 @@ skip:
double_unlock_balance(this_rq, src_rq);
}

+ put_online_cpus_atomic();
return ret;
}


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