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

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Date:	Mon, 8 Aug 2016 12:22:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Bart Van Assche <bart.vanassche@...disk.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"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 Fri, Aug 05, 2016 at 10:41:33AM -0700, Bart Van Assche wrote:
> On 08/04/2016 07:09 AM, Peter Zijlstra wrote:

> >But I'd still like to understand where we loose the wakeup.
> 
> My assumption is that __wake_up_common() and signal delivery happen
> concurrently, that __wake_up_common() wakes up bit_wait_io() and that signal
> delivery happens after bit_wait_io() has been woken up but before it tests
> the signal pending state.

That would be the exact scenario I drew a picture of, no? I'm still
failing to see the hole there.

Please draw a picture like that and illustrate the hole.