[PATCH 2/2] mm: don't hide potentially null memmap pointer in sparse_remove_section

From: Alastair D'Silva
Date: Tue Aug 27 2019 - 01:37:33 EST


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.

This patch passes the offset to clear_hwpoisoned_pages instead, allowing
memmap to successfully perform it's null check.

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