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Date:   Mon, 28 Jan 2019 19:45:28 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Mikhail Zaslonko <zaslonko@linux.ibm.com>,
        Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com,
        gerald.schaefer@de.ibm.com, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/2] mm, memory_hotplug: fix uninitialized pages fallouts.
Message-ID: <20190128184528.GU18811@dhcp22.suse.cz>
References: <20190128144506.15603-1-mhocko@kernel.org>
 <20190128095054.4103093dec81f1c904df7929@linux-foundation.org>
 <20190128184139.GR18811@dhcp22.suse.cz>
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On Mon 28-01-19 19:41:39, Michal Hocko wrote:
> On Mon 28-01-19 09:50:54, Andrew Morton wrote:
> > On Mon, 28 Jan 2019 15:45:04 +0100 Michal Hocko <mhocko@kernel.org> wrote:
> > 
> > > Mikhail has posted fixes for the two bugs quite some time ago [1]. I
> > > have pushed back on those fixes because I believed that it is much
> > > better to plug the problem at the initialization time rather than play
> > > whack-a-mole all over the hotplug code and find all the places which
> > > expect the full memory section to be initialized. We have ended up with
> > > 2830bf6f05fb ("mm, memory_hotplug: initialize struct pages for the full
> > > memory section") merged and cause a regression [2][3]. The reason is
> > > that there might be memory layouts when two NUMA nodes share the same
> > > memory section so the merged fix is simply incorrect.
> > > 
> > > In order to plug this hole we really have to be zone range aware in
> > > those handlers. I have split up the original patch into two. One is
> > > unchanged (patch 2) and I took a different approach for `removable'
> > > crash. It would be great if Mikhail could test it still works for his
> > > memory layout.
> > > 
> > > [1] http://lkml.kernel.org/r/20181105150401.97287-2-zaslonko@linux.ibm.com
> > > [2] https://bugzilla.redhat.com/show_bug.cgi?id=1666948
> > > [3] http://lkml.kernel.org/r/20190125163938.GA20411@dhcp22.suse.cz
> > 
> > Any thoughts on which kernel version(s) need these patches?
> 
> My remark in 2830bf6f05fb still holds
>     : This has alwways been problem AFAIU.  It just went unnoticed because we
>     : have zeroed memmaps during allocation before f7f99100d8d9 ("mm: stop
>     : zeroing memory during allocation in vmemmap") and so the above test
>     : would simply skip these ranges as belonging to zone 0 or provided a
>     : garbage.
>     :
>     : So I guess we do care for post f7f99100d8d9 kernels mostly and
>     : therefore Fixes: f7f99100d8d9 ("mm: stop zeroing memory during
>     : allocation in vmemmap")
> 
> But, please let's wait for the patch 1 to be confirmed to fix the issue.

Also the revert [1] should be applied first. I thought Linus would pick
it up but he hasn't done so yet.

[1] http://lkml.kernel.org/r/20190125181549.GE20411@dhcp22.suse.cz
-- 
Michal Hocko
SUSE Labs