linux-kernel - Re: [PATCH 7/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case

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Date:   Mon, 10 Feb 2020 11:41:05 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, dan.j.williams@...el.com,
        david@...hat.com
Subject: Re: [PATCH 7/7] mm/hotplug: fix hot remove failure in
 SPARSEMEM|!VMEMMAP case

On 02/10/20 at 07:52am, Wei Yang wrote:
> >---
> > mm/sparse.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> >diff --git a/mm/sparse.c b/mm/sparse.c
> >index 623755e88255..345d065ef6ce 100644
> >--- a/mm/sparse.c
> >+++ b/mm/sparse.c
> >@@ -854,13 +854,15 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> > 			ms->usage = NULL;
> > 		}
> > 		memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
> >-		ms->section_mem_map = (unsigned long)NULL;
> > 	}
> > 
> > 	if (section_is_early && memmap)
> > 		free_map_bootmem(memmap);
> > 	else
> > 		depopulate_section_memmap(pfn, nr_pages, altmap);
> 
> The crash happens in depopulate_section_memmap() when trying to get memmap by
> pfn_to_page(). Can we pass memmap directly?

Yes, that's also a good idea. While it needs to add a parameter for
depopulate_section_memmap(), the parameter is useless for VMEMMAP
though, I personally prefer the current fix which is a little simpler.

Anyway, both is fine to me, I can update if you think passing memmap is
better.

> 
> >+
> >+	if(!rc)
> >+		ms->section_mem_map = (unsigned long)NULL;
> > }
> > 
> > static struct page * __meminit section_activate(int nid, unsigned long pfn,
> >-- 
> >2.17.2
> 
> -- 
> Wei Yang
> Help you, Help me
>