sched: Add TASK_WAKING
We're going to want to drop rq->lock in try_to_wake_up() for a longer period of time, however we also want to deal with concurrent waking of the same task, which is currently handled by holding rq->lock. So introduce a new TASK state, namely TASK_WAKING, which indicates someone is already waking the task (other wakers will fail p->state & state). We also keep preemption disabled over the whole ttwu(). Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -190,6 +190,7 @@ extern unsigned long long time_sync_thresh;
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/* in tsk->state again */
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#define TASK_DEAD 64
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#define TASK_WAKEKILL 128
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#define TASK_WAKING 256
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/* Convenience macros for the sake of set_task_state */
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#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
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@ -2310,7 +2310,6 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
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{
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int cpu, orig_cpu, this_cpu, success = 0;
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unsigned long flags;
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long old_state;
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struct rq *rq;
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if (!sched_feat(SYNC_WAKEUPS))
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@ -2332,11 +2331,12 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
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}
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#endif
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this_cpu = get_cpu();
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smp_wmb();
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rq = task_rq_lock(p, &flags);
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update_rq_clock(rq);
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old_state = p->state;
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if (!(old_state & state))
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if (!(p->state & state))
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goto out;
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if (p->se.on_rq)
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@ -2344,27 +2344,25 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
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cpu = task_cpu(p);
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orig_cpu = cpu;
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this_cpu = smp_processor_id();
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#ifdef CONFIG_SMP
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if (unlikely(task_running(rq, p)))
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goto out_activate;
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cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, sync);
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if (cpu != orig_cpu) {
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set_task_cpu(p, cpu);
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/*
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* In order to handle concurrent wakeups and release the rq->lock
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* we put the task in TASK_WAKING state.
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*/
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p->state = TASK_WAKING;
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task_rq_unlock(rq, &flags);
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/* might preempt at this point */
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rq = task_rq_lock(p, &flags);
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old_state = p->state;
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if (!(old_state & state))
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goto out;
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if (p->se.on_rq)
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goto out_running;
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this_cpu = smp_processor_id();
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cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, sync);
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if (cpu != orig_cpu)
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set_task_cpu(p, cpu);
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rq = task_rq_lock(p, &flags);
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WARN_ON(p->state != TASK_WAKING);
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cpu = task_cpu(p);
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}
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#ifdef CONFIG_SCHEDSTATS
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schedstat_inc(rq, ttwu_count);
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@ -2422,6 +2420,7 @@ out_running:
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#endif
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out:
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task_rq_unlock(rq, &flags);
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put_cpu();
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return success;
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}
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