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

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Message-ID: <CA+55aFx67j0u=GNRKoCWpsLRDcHdrjfVvWRS067wLUSfzstgoQ@mail.gmail.com>
Date:   Fri, 25 Aug 2017 16:03:50 -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 Fri, Aug 25, 2017 at 3:51 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So take it as that: example pseudo-code that happens to pass a
> compiler, but is meant as a RFD rather than actually working.

Oh, and after I sent it out, I wanted to look once again, and realized
that the "remove_myself_from()" function is entirely broken.

The caller has already removed the page entry, we don't want to remove
it again, we want to add a *new* one with us removed from it.

So here's an updated 2/2 patch with that fixed.

Let this be a lesson in just *how* little tested, and *how* crap that
patch probably still is.

                 Linus

View attachment "0002-Re-implement-the-page-bit-wait-code.patch" of type "text/x-patch" (13238 bytes)