linux-kernel - Re: [PATCH v2 0/4] task: Making tasks on the runqueue rcu protected

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Message-ID: <8736gu962r.fsf@x220.int.ebiederm.org>
Date:   Tue, 17 Sep 2019 12:38:04 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Christoph Lameter <cl@...ux.com>,
        Kirill Tkhai <tkhai@...dex.ru>, Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v2 0/4] task: Making tasks on the runqueue rcu protected

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Sat, Sep 14, 2019 at 5:30 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>>
>> I have reworked these patches one more time to make it clear that the
>> first 3 patches only fix task_struct so that it experiences a rcu grace
>> period after it leaves the runqueue for the last time.
>
> I remain a fan of these patches, and the added comment on the last one
> is I think a sufficient clarification of the issue.
>
> But it's patch 3 that makes me go "yeah, this is the right approach",
> because it just removes subtle code in favor of something that is
> understandable.
>
> Yes, most of the lines removed may be comments, and so it doesn't
> actually remove a lot of _code_, but I think the comments are a result
> of just how subtle and fragile our current approach is, and the new
> model not needing them as much is I think a real issue (rather than
> just Eric being less verbose in the new comments and removing lines of
> code that way).

In fact the comments I add are orthogonal to the comments I removed.
My last patch stands on it's own.  It can be applied with or without the
rest.   I just needed to know which of the ordinary rcu guarantees were
or were not present in the code.

> Can anybody see anything wrong with the series? Because I'd love to
> have it for 5.4,

Peter,

I am more than happy for these to come through your tree.  However
if this is one thing to many I will be happy to send Linus a pull
request myself early next week.

Eric