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Date:   Thu, 26 Apr 2018 21:11:11 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Pavel Tatashin <pasha.tatashin@oracle.com>
Cc:     steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
        akpm@linux-foundation.org, kirill.shutemov@linux.intel.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: sections are not offlined during memory hotremove
Message-ID: <20180426191111.GV17484@dhcp22.suse.cz>
References: <20180426155834.16845-1-pasha.tatashin@oracle.com>
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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@oracle.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  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