linux-kernel - Re: [PATCH 2/2] ras: close the race condition with timer

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Message-ID: <CAM_iQpWPq8p3L1v_h0_iEkq4Lcw=E84boZEQYUJxxuJtgHDo9w@mail.gmail.com>
Date:   Tue, 16 Apr 2019 11:00:32 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-edac@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] ras: close the race condition with timer

On Tue, Apr 16, 2019 at 10:43 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Apr 16, 2019 at 10:09:49AM -0700, Cong Wang wrote:
> > They are just locks requiring different contexts, I don't see how one is
> > simpler than the other. Do you mind to be more specific?
>
> Yes, I'd like for this whole CEC code to be lazy and preemptible as it
> is not at all important when it does its work, as long as it gets it
> done eventually.
>
> Can't be preemptible with spinlocks.

Got it, but the work done with holding a spinlock isn't heavy, given
there are only at most 512 elements in the array.

>
> > By workqueue, you must mean to say delayed work, right?
> >
> > But the global workqueue is not serialized either,
>
> Serialized with what? Insertions?

Hmm? We still have to serialize either the timer callback or
a delayed work with the rest of array updates (add or delete),
right?

As far as I understand, two works in the global workqueue could
be still ran in parallel on different CPU's, this is why I said it has to
be an ordered queue to guarantee the serialization.


>
> That's what the mutex is for and the insertions happen in process
> context.
>
> So yeah, delayed_work sounds like what it should do. I.e.,
> queue_delayed_work() and decay_interval_set() should do
> mod_delayed_work(). Something along those lines, anyways.

This part is perfectly understood.

Thanks.