linux-kernel - Re: [PATCH 2/2 v2] sched/wait: Introduce lock breaker in wake_up_page

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Message-ID: <CA+55aFzmQe+Q60jjEKmu=Jv-wUCgeAeErp6ANbSmfO45j7Q8ZA@mail.gmail.com>
Date:   Sun, 27 Aug 2017 14:42:11 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        Christopher Lameter <cl@...ux.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2 v2] sched/wait: Introduce lock breaker in wake_up_page_bit

On Sun, Aug 27, 2017 at 2:40 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> End result: page is unlocked, CPU3 is waiting, nothing will wake CPU3 up.

Not CPU3. CPU3 was the waker. It's thread 2 that is waiting and never
got woken up, of course.

Other than that, the scenario still looks real to me.

Ideas?

                 Linus