On Tue 27-08-19 15:36:55, Alastair D'Silva wrote:
> From: Alastair D'Silva <alastair@xxxxxxxxxxx>
>
> By adding offset to memmap before passing it in to clear_hwpoisoned_pages,
> we hide a theoretically null memmap from the null check inside
> clear_hwpoisoned_pages.
Isn't that other way around? Calculating the offset struct page pointer
will actually make the null check effective. Besides that I cannot
really see how pfn_to_page would return NULL. I have to confess that I
cannot really see how offset could lead to a NULL struct page either and
I strongly suspect that the NULL check is not really needed. Maybe it
used to be in the past.
> This patch passes the offset to clear_hwpoisoned_pages instead, allowing
> memmap to successfully perform it's null check.
I do not see any improvement in this patch. It just adds a new argument
unnecessarily.
> Signed-off-by: Alastair D'Silva <alastair@xxxxxxxxxxx>
> ---
> mm/sparse.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index e41917a7e844..3ff84e627e58 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -882,7 +882,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
> }
>
> #ifdef CONFIG_MEMORY_FAILURE
> -static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
> +static void clear_hwpoisoned_pages(struct page *memmap, int start, int count)
> {
> int i;
>
> @@ -898,7 +898,7 @@ 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++) {
> if (PageHWPoison(&memmap[i])) {
> num_poisoned_pages_dec();
> ClearPageHWPoison(&memmap[i]);
> @@ -906,7 +906,8 @@ 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, int start,
> + int count)
> {
> }
> #endif
> @@ -915,7 +916,7 @@ void sparse_remove_section(struct mem_section *ms, unsigned long pfn,
> unsigned long nr_pages, unsigned long map_offset,
> struct vmem_altmap *altmap)
> {
> - clear_hwpoisoned_pages(pfn_to_page(pfn) + map_offset,
> + clear_hwpoisoned_pages(pfn_to_page(pfn), map_offset,
> nr_pages - map_offset);
> section_deactivate(pfn, nr_pages, altmap);
> }
> --
> 2.21.0
>
--
Michal Hocko
SUSE Labs
