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Subject[RFC][PATCH 10/17] sched: Add TASK_WAKING to task_rq_lock
In order to be able to call set_task_cpu() without holding the
appropriate rq->lock during ttwu(), add a TASK_WAKING clause to the
task_rq_lock() primitive.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/sched.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -928,12 +928,13 @@ static inline void finish_lock_switch(st
#endif /* __ARCH_WANT_UNLOCKED_CTXSW */

/*
- * Check whether the task is waking, we use this to synchronize ->cpus_allowed
- * against ttwu().
+ * In order to be able to call set_task_cpu() without holding the current
+ * task_rq(p)->lock during wake-ups we need to serialize on something else,
+ * use the wakeup task state.
*/
static inline int task_is_waking(struct task_struct *p)
{
- return unlikely(p->state == TASK_WAKING);
+ return p->state == TASK_WAKING;
}

/*
@@ -948,7 +949,7 @@ static inline struct rq *__task_rq_lock(
for (;;) {
rq = task_rq(p);
raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p)))
+ if (likely(rq == task_rq(p) && !task_is_waking(p)))
return rq;
raw_spin_unlock(&rq->lock);
}
@@ -956,8 +957,7 @@ static inline struct rq *__task_rq_lock(

/*
* task_rq_lock - lock the runqueue a given task resides on and disable
- * interrupts. Note the ordering: we can safely lookup the task_rq without
- * explicitly disabling preemption.
+ * interrupts.
*/
static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
__acquires(rq->lock)
@@ -968,7 +968,7 @@ static struct rq *task_rq_lock(struct ta
local_irq_save(*flags);
rq = task_rq(p);
raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p)))
+ if (likely(rq == task_rq(p) && !task_is_waking(p)))
return rq;
raw_spin_unlock_irqrestore(&rq->lock, *flags);
}



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