linux-kernel - Re: [PATCH] mm: sections are not offlined during memory hotremove

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Message-ID: <20180426191152.GW17484@dhcp22.suse.cz>
Date:   Thu, 26 Apr 2018 21:11:52 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: sections are not offlined during memory hotremove

On Thu 26-04-18 21:11:11, Michal Hocko wrote:
> On Thu 26-04-18 11:58:34, Pavel Tatashin wrote:
> > Memory hotplug, and hotremove operate with per-block granularity. If
> > machine has large amount of memory (more than 64G), the size of memory
> > block can span multiple sections. By mistake, during hotremove we set
> > only the first section to offline state.
> > 
> > The bug was discovered because kernel selftest started to fail:
> > https://lkml.kernel.org/r/20180423011247.GK5563@yexl-desktop
> > 
> > After commit, "mm/memory_hotplug: optimize probe routine". But, the bug is
> > older than this commit. In this optimization we also added a check for
> > sections to be in a proper state during hotplug operation.
> > 
> > Fixes: 2d070eab2e82 ("mm: consider zone which is not fully populated to have holes")
> 
> Dohh. When I saw this I've had that feeling that I have fixed this
> already and it must have get lost somewhere. But no, this was the same
> bug in a different path b4ccec41af82 ("mm/sparse.c: fix typo in
> online_mem_sections"). I wonder why I haven't noticed the same pattern
> in the offline path.
> 
> Thanks for noticing and fixing this.
> 
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> 
> Acked-by: Michal Hocko <mhocko@...e.com>

Btw. Cc: stable would be appropriate.

> 
> >  mm/sparse.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 62eef264a7bd..73dc2fcc0eab 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -629,7 +629,7 @@ void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
> >  	unsigned long pfn;
> >  
> >  	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> > -		unsigned long section_nr = pfn_to_section_nr(start_pfn);
> > +		unsigned long section_nr = pfn_to_section_nr(pfn);
> >  		struct mem_section *ms;
> >  
> >  		/*
> > -- 
> > 1.8.3.1
> > 
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs