linux-kernel - Re: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree

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Message-ID: <Ybm91+/z8hKuiHYr@dhcp22.suse.cz>
Date:   Wed, 15 Dec 2021 11:05:11 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dennis Zhou <dennis@...nel.org>,
        Alexey Makhalov <amakhalov@...are.com>,
        "cl@...ux.com" <cl@...ux.com>,
        "mm-commits@...r.kernel.org" <mm-commits@...r.kernel.org>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "tj@...nel.org" <tj@...nel.org>
Subject: Re: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree

On Tue 14-12-21 12:57:48, Andrew Morton wrote:
> On Tue, 14 Dec 2021 11:11:54 +0100 Michal Hocko <mhocko@...e.com> wrote:
> 
> > > I need some clarification here. It sounds like memoryless nodes work on
> > > x86, but hotplug + memoryless nodes isn't a supported use case or you're
> > > introducing it as a new use case?
> > > 
> > > If this is a new use case, then I'm inclined to say this patch should
> > > NOT go in and a proper fix should be implemented on hotplug's side. I
> > > don't want to be in the business of having/seeing this conversation
> > > reoccur because we just papered over this issue in percpu.
> > 
> > The patch still seems to be in the mmotm tree. I have sent a different
> > fix candidate [1] which should be more robust and cover also other potential
> > places.
> > 
> > [1] http://lkml.kernel.org/r/20211214100732.26335-1-mhocko@kernel.org
> 
> Is cool, I'm paying attention.
> 
> We do want something short and simple for backporting to -stable (like
> Alexey's patch) so please bear that in mind while preparing an
> alternative.

I think we want something that fixes the underlying problem. Please keep
in mind that the pcp allocation is not the only place to hit the issue.
We have more. I do not want we want to handle each and every one
separately.

I am definitly not going to push for my solution but if there is a
consensus this is the right approach then I do not think we really want
to implement these partial workarounds.

-- 
Michal Hocko
SUSE Labs