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Subject[PATCH -rt 1/1] sched_rt: change spinlock primitive in post_schedule_rt()
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In the function post_schedule_rt() of the current preempt-rt kernel,
push_rt_task() is surrounded by atomic_spin_lock_irq(&rq->lock) and
atomic_spin_unlock_irq(&rq->lock), which means that the function is
called with the runqueue lock held and the interrupt disabled.

A problem is that after finishing post_schedule_rt(), interrupt is always
re-enabled regardless of the previous condition. In practice, the function
post_schedule_rt() is called by finish_task_switch() with the interrupt disabled.
Thus, the interrupt should not be re-enabled at the moment.

The problem can simply be resolved by replacing atomic_spin_lock_irq() and
atomic_spin_unlock_irq() with atomic_spin_lock_irqsave() and
atomic_spin_unlock_irqrestore().

As a sidenote, the other way to resolve the problem might be to modify codes
in accordance with commit 3f029d3c6d62068d59301d90c18dbde8ee402107, titled
"sched: Enhance the pre/post scheduling logic", in the vanilla tree.

Signed-off-by: Jupyung Lee <jupyung@gmail.com>
---
kernel/sched_rt.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 274c976..bd16998 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1536,9 +1536,10 @@ static void post_schedule_rt(struct rq *rq)
* This is only called if needs_post_schedule_rt() indicates that
* we need to push tasks away
*/
- atomic_spin_lock_irq(&rq->lock);
+ unsigned long flags;
+ atomic_spin_lock_irqsave(&rq->lock, flags);
push_rt_tasks(rq);
- atomic_spin_unlock_irq(&rq->lock);
+ atomic_spin_unlock_irqrestore(&rq->lock, flags);
}

/*
--
1.6.5.GIT


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