mm/rmap.c: fix pgoff calculation to handle hugepage correctly

I triggered VM_BUG_ON() in vma_address() when I tried to migrate an
anonymous hugepage with mbind() in the kernel v3.16-rc3.  This is
because pgoff's calculation in rmap_walk_anon() fails to consider
compound_order() only to have an incorrect value.

This patch introduces page_to_pgoff(), which gets the page's offset in
PAGE_CACHE_SIZE.

Kirill pointed out that page cache tree should natively handle
hugepages, and in order to make hugetlbfs fit it, page->index of
hugetlbfs page should be in PAGE_CACHE_SIZE.  This is beyond this patch,
but page_to_pgoff() contains the point to be fixed in a single function.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 5 insertions, 9 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index c6399e328931..7211a73ba14d 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -435,7 +435,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
         if (av == NULL) /* Not actually mapped anymore */
                 return;
 
-        pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+        pgoff = page_to_pgoff(page);
         read_lock(&tasklist_lock);
         for_each_process (tsk) {
                 struct anon_vma_chain *vmac;
@@ -469,7 +469,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
         mutex_lock(&mapping->i_mmap_mutex);
         read_lock(&tasklist_lock);
         for_each_process(tsk) {
-                pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+                pgoff_t pgoff = page_to_pgoff(page);
                 struct task_struct *t = task_early_kill(tsk, force_early);
 
                 if (!t)
diff --git a/mm/rmap.c b/mm/rmap.c
index b7e94ebbd09e..22a4a7699cdb 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -517,11 +517,7 @@ void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
 static inline unsigned long
 __vma_address(struct page *page, struct vm_area_struct *vma)
 {
-        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
-
-        if (unlikely(is_vm_hugetlb_page(vma)))
-                pgoff = page->index << huge_page_order(page_hstate(page));
-
+        pgoff_t pgoff = page_to_pgoff(page);
         return vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
 }
 
@@ -1639,7 +1635,7 @@ static struct anon_vma *rmap_walk_anon_lock(struct page *page,
 static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
 {
         struct anon_vma *anon_vma;
-        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+        pgoff_t pgoff = page_to_pgoff(page);
         struct anon_vma_chain *avc;
         int ret = SWAP_AGAIN;
 
@@ -1680,7 +1676,7 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
 static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
 {
         struct address_space *mapping = page->mapping;
-        pgoff_t pgoff = page->index << compound_order(page);
+        pgoff_t pgoff = page_to_pgoff(page);
         struct vm_area_struct *vma;
         int ret = SWAP_AGAIN;