workqueue: skip nr_running sanity check in worker_enter_idle() if trustee is active
worker_enter_idle() has WARN_ON_ONCE() which triggers if nr_running isn't zero when every worker is idle. This can trigger spuriously while a cpu is going down due to the way trustee sets %WORKER_ROGUE and zaps nr_running. It first sets %WORKER_ROGUE on all workers without updating nr_running, releases gcwq->lock, schedules, regrabs gcwq->lock and then zaps nr_running. If the last running worker enters idle inbetween, it would see stale nr_running which hasn't been zapped yet and trigger the WARN_ON_ONCE(). Fix it by performing the sanity check iff the trustee is idle. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: stable@vger.kernel.org
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@ -1213,8 +1213,13 @@ static void worker_enter_idle(struct worker *worker)
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} else
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wake_up_all(&gcwq->trustee_wait);
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/* sanity check nr_running */
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WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle &&
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/*
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* Sanity check nr_running. Because trustee releases gcwq->lock
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* between setting %WORKER_ROGUE and zapping nr_running, the
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* warning may trigger spuriously. Check iff trustee is idle.
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*/
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WARN_ON_ONCE(gcwq->trustee_state == TRUSTEE_DONE &&
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gcwq->nr_workers == gcwq->nr_idle &&
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atomic_read(get_gcwq_nr_running(gcwq->cpu)));
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}
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