Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs

[Peter Zijlstra]

On Wed, Aug 10, 2016 at 12:57:25PM +0200, Oleg Nesterov wrote:
> This condition is fine, and the trace is clear. This means that lock_page_killable()
> was interrupted and wake_bit_function() was not called. We do not need another wakeup
> in this case but somehow it helps. Again, I think because the necessary wakeup was
> already lost/missed.

I suspect the same. Removing that else generates 'spurious' wakeups,
which can unstick the situation, hiding the real source of the problem.