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SubjectRe: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check
On 03/25/20 at 03:06pm, Baoquan He wrote:
> On 03/25/20 at 08:49am, Aneesh Kumar K.V wrote:

> > mm/sparse.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index aadb7298dcef..3012d1f3771a 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -781,6 +781,8 @@ 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);
> > + /* Mark the section invalid */
> > + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
>
> Not sure if we should add checking in valid_section() or pfn_valid(),
> e.g check ms->usage validation too. Otherwise, this fix looks good to
> me.

With SPASEMEM_VMEMAP enabled, we should do validation check on ms->usage
before checking any subsection is valid. Since now we do have case
in which ms->usage is released, people still try to check it.

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index f0a2c184eb9a..d79bd938852e 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1306,6 +1306,8 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
{
int idx = subsection_map_index(pfn);

+ if (!ms->usage)
+ return 0;
return test_bit(idx, ms->usage->subsection_map);
}
#else
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