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Subject[RFC][PATCH 12/17] sched: Also serialize ttwu_local() with p->pi_lock
Since we now serialize ttwu() using p->pi_lock, we also need to
serialize ttwu_local() using that, otherwise, once we drop the
rq->lock from ttwu() it can race with ttwu_local().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/sched.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2513,9 +2513,9 @@ static int try_to_wake_up(struct task_st
* try_to_wake_up_local - try to wake up a local task with rq lock held
* @p: the thread to be awakened
*
- * Put @p on the run-queue if it's not alredy there. The caller must
+ * Put @p on the run-queue if it's not alredy there. The caller must
* ensure that this_rq() is locked, @p is bound to this_rq() and not
- * the current task. this_rq() stays locked over invocation.
+ * the current task.
*/
static void try_to_wake_up_local(struct task_struct *p)
{
@@ -2523,16 +2523,21 @@ static void try_to_wake_up_local(struct

BUG_ON(rq != this_rq());
BUG_ON(p == current);
- lockdep_assert_held(&rq->lock);
+
+ raw_spin_unlock(&rq->lock);
+ raw_spin_lock(&p->pi_lock);
+ raw_spin_lock(&rq->lock);

if (!(p->state & TASK_NORMAL))
- return;
+ goto out;

if (!p->on_rq)
activate_task(rq, p, ENQUEUE_WAKEUP);

ttwu_post_activation(p, rq, 0);
ttwu_stat(rq, p, smp_processor_id(), 0);
+out:
+ raw_spin_unlock(&p->pi_lock);
}

/**
@@ -3925,6 +3930,7 @@ pick_next_task(struct rq *rq)
*/
asmlinkage void __sched schedule(void)
{
+ struct task_struct *to_wakeup = NULL;
struct task_struct *prev, *next;
unsigned long *switch_count;
struct rq *rq;
@@ -3958,21 +3964,21 @@ asmlinkage void __sched schedule(void)
* task to maintain concurrency. If so, wake
* up the task.
*/
- if (prev->flags & PF_WQ_WORKER) {
- struct task_struct *to_wakeup;
-
+ if (prev->flags & PF_WQ_WORKER)
to_wakeup = wq_worker_sleeping(prev, cpu);
- if (to_wakeup)
- try_to_wake_up_local(to_wakeup);
- }
deactivate_task(rq, prev, DEQUEUE_SLEEP);
prev->on_rq = 0;
}
switch_count = &prev->nvcsw;
}

+ /*
+ * All three: try_to_wake_up_local(), pre_schedule() and idle_balance()
+ * can drop rq->lock.
+ */
+ if (to_wakeup)
+ try_to_wake_up_local(to_wakeup);
pre_schedule(rq, prev);
-
if (unlikely(!rq->nr_running))
idle_balance(cpu, rq);




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