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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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