linux-kernel - Re: [PATCH v3] mm: fix tick timer stall during deferred page init

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Message-ID: <CA+CK2bCGpG6kBjkGd-QP06kNtwezj8mW13Jdvbxs6ExzRaJSpQ@mail.gmail.com>
Date:   Wed, 1 Apr 2020 12:41:13 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] mm: fix tick timer stall during deferred page init

On Wed, Apr 1, 2020 at 12:26 PM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Wed 01-04-20 12:18:10, Daniel Jordan wrote:
> > On Wed, Apr 01, 2020 at 06:12:43PM +0200, Michal Hocko wrote:
> > > On Wed 01-04-20 12:09:29, Daniel Jordan wrote:
> > > > On Wed, Apr 01, 2020 at 06:00:48PM +0200, Michal Hocko wrote:
> > > > > On Wed 01-04-20 17:50:22, David Hildenbrand wrote:
> > > > > > On 01.04.20 17:42, Michal Hocko wrote:
> > > > > > > This needs a double checking but I strongly believe that the lock can be
> > > > > > > simply dropped in this path.
> > > >
> > > > This is what my fix does, it limits the time the resize lock is held.
> > >
> > > Just remove it from the deferred intialization and add a comment that we
> > > deliberately not taking the lock here because abc
> >
> > I think it has to be a little more involved because of the window where
> > interrupts might allocate during deferred init, as Vlastimil pointed out a few
> > years ago when the change was made.
>
> I do not remember any details but do we have any actual real allocation
> failure or was this mostly a theoretical concern. Vlastimil? For your
> context we are talking about 3a2d7fa8a3d5 ("mm: disable interrupts while
> initializing deferred pages")

I do not remember seeing any real failures, this was a theoretical
window. So, we could potentially simply remove these locks until we
see a real boot failure in some interrupt thread. The allocation has
to be rather large as well.

Pasha