[PATCH wq/for-4.0-fixes v2] workqueue: fix hang involving racing cancel[_delayed]_work_sync()'s for PREEMPT_NONE

[Tejun Heo]

Hello,

Found the culprit.  Plain wake_up() shouldn't be used on
bit_waitqueues.  The following patch should fix the issue.  I replaced
the patch in the wq branches.

Thanks a lot.

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