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SubjectRe: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check
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On 3/25/20 1:07 PM, Baoquan He wrote:
> 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
>

We always check for section valid, before we check if pfn_section_valid().

static inline int pfn_valid(unsigned long pfn)

struct mem_section *ms;

if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
return 0;
ms = __nr_to_section(pfn_to_section_nr(pfn));
if (!valid_section(ms))
return 0;
/*
* Traditionally early sections always returned pfn_valid() for
* the entire section-sized span.
*/
return early_section(ms) || pfn_section_valid(ms, pfn);
}


IMHO adding that if (!ms->usage) is redundant.

-aneesh


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