linux-kernel - Re: [PATCH] sched: Avoid that __wait_on_bit

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Message-ID: <20160810110357.GL30192@twins.programming.kicks-ass.net>
Date:	Wed, 10 Aug 2016 13:03:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Bart Van Assche <bart.vanassche@...disk.com>,
	Bart Van Assche <bvanassche@....org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Neil Brown <neilb@...e.de>,
	Michael Shaver <jmshaver@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs

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.