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    SubjectRe: [PATCH v2 2/3] mm: don't hide potentially null memmap pointer in sparse_remove_one_section
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    On 26.06.19 08:11, Alastair D'Silva wrote:
    > From: Alastair D'Silva <alastair@d-silva.org>
    >
    > By adding offset to memmap before passing it in to clear_hwpoisoned_pages,
    > we hide a potentially null memmap from the null check inside
    > clear_hwpoisoned_pages.
    >
    > This patch passes the offset to clear_hwpoisoned_pages instead, allowing
    > memmap to successfully peform it's null check.
    >
    > Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
    > ---
    > mm/sparse.c | 10 ++++++----
    > 1 file changed, 6 insertions(+), 4 deletions(-)
    >
    > diff --git a/mm/sparse.c b/mm/sparse.c
    > index 57a1a3d9c1cf..1ec32aef5590 100644
    > --- a/mm/sparse.c
    > +++ b/mm/sparse.c
    > @@ -753,7 +753,8 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
    >
    > #ifdef CONFIG_MEMORY_HOTREMOVE
    > #ifdef CONFIG_MEMORY_FAILURE
    > -static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
    > +static void clear_hwpoisoned_pages(struct page *memmap,
    > + unsigned long start, unsigned long count)
    > {
    > int i;
    >
    > @@ -769,7 +770,7 @@ static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
    > if (atomic_long_read(&num_poisoned_pages) == 0)
    > return;
    >
    > - for (i = 0; i < nr_pages; i++) {
    > + for (i = start; i < start + count; i++) {

    start and count are unsigned long's, i is an int.

    Besides that

    Acked-by: David Hildenbrand <david@redhat.com>

    > if (PageHWPoison(&memmap[i])) {
    > atomic_long_sub(1, &num_poisoned_pages);
    > ClearPageHWPoison(&memmap[i]);
    > @@ -777,7 +778,8 @@ static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
    > }
    > }
    > #else
    > -static inline void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
    > +static inline void clear_hwpoisoned_pages(struct page *memmap,
    > + unsigned long start, unsigned long count)
    > {
    > }
    > #endif
    > @@ -824,7 +826,7 @@ void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
    > ms->pageblock_flags = NULL;
    > }
    >
    > - clear_hwpoisoned_pages(memmap + map_offset,
    > + clear_hwpoisoned_pages(memmap, map_offset,
    > PAGES_PER_SECTION - map_offset);
    > free_section_usemap(memmap, usemap, altmap);
    > }
    >


    --

    Thanks,

    David / dhildenb

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