3.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andy Lutomirski <l...@amacapital.net>
commit fd7de1e8d5b2b2b35e71332fafb899f584597150 upstream.
Locklessly doing is_idle_task(rq->curr) is only okay because of
RCU protection. The older variant of the broken code checked
rq->curr == rq->idle instead and therefore didn't need RCU.
Fixes: f6be8af1c95d ("sched: Add new API wake_up_if_idle() to wake up the idle
cpu")
Signed-off-by: Andy Lutomirski <l...@amacapital.net>
Reviewed-by: Chuansheng Liu <chuansheng....@intel.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Link:
http://lkml.kernel.org/r/729365dddca178506dfd0a9451006344cd6808bc.1417277372.git.l...@amacapital.net
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
kernel/sched/core.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1623,8 +1623,10 @@ void wake_up_if_idle(int cpu)
struct rq *rq = cpu_rq(cpu);
unsigned long flags;
- if (!is_idle_task(rq->curr))
- return;
+ rcu_read_lock();
+
+ if (!is_idle_task(rcu_dereference(rq->curr)))
+ goto out;
if (set_nr_if_polling(rq->idle)) {
trace_sched_wake_idle_without_ipi(cpu);
@@ -1635,6 +1637,9 @@ void wake_up_if_idle(int cpu)
/* Else cpu is not in idle, do nothing here */
raw_spin_unlock_irqrestore(&rq->lock, flags);
}
+
+out:
+ rcu_read_unlock();
}
bool cpus_share_cache(int this_cpu, int that_cpu)
--
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