mm: fix __page_to_pfn for a const struct page argument

This allows the cast in lowmem_page_address (introduced as a warning
fixup to 33dd4e0ec911 "mm: make some struct page's const") to be
removed.

Propagate const'ness to page_to_section() as well since it is required
by __page_to_pfn.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 4 insertions, 4 deletions

diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
index fb2d63f13f4c..aea9e45efce6 100644
--- a/include/asm-generic/memory_model.h
+++ b/include/asm-generic/memory_model.h
@@ -39,7 +39,7 @@
 })
 
 #define __page_to_pfn(pg)                                               \
-({      struct page *__pg = (pg);                                       \
+({      const struct page *__pg = (pg);                                 \
         struct pglist_data *__pgdat = NODE_DATA(page_to_nid(__pg));     \
         (unsigned long)(__pg - __pgdat->node_mem_map) +                 \
          __pgdat->node_start_pfn;                                       \
@@ -57,7 +57,7 @@
  * section[i].section_mem_map == mem_map's address - start_pfn;
  */
 #define __page_to_pfn(pg)                                       \
-({      struct page *__pg = (pg);                               \
+({      const struct page *__pg = (pg);                         \
         int __sec = page_to_section(__pg);                      \
         (unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec))); \
 })
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c06454d60a3d..7438071b44aa 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -685,7 +685,7 @@ static inline void set_page_section(struct page *page, unsigned long section)
         page->flags |= (section & SECTIONS_MASK) << SECTIONS_PGSHIFT;
 }
 
-static inline unsigned long page_to_section(struct page *page)
+static inline unsigned long page_to_section(const struct page *page)
 {
         return (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
 }
@@ -720,7 +720,7 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
 
 static __always_inline void *lowmem_page_address(const struct page *page)
 {
-        return __va(PFN_PHYS(page_to_pfn((struct page *)page)));
+        return __va(PFN_PHYS(page_to_pfn(page)));
 }
 
 #if defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL)