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authorAndrew Morton <akpm@linux-foundation.org>2014-12-18 16:17:29 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-18 19:08:11 -0800
commitd82fa87d2b60e8affea3b244ad23c5d9a59c584a (patch)
treee989c53dc22e9adc967880171c805df3a85048aa
parent48332f28461c72af4b98611e0b4f02d769b8cc70 (diff)
mm/memory.c:do_shared_fault(): add comment
Belatedly document the changes in commit f0c6d4d295e4 ("mm: introduce do_shared_fault() and drop do_fault()"). Cc: Andi Kleen <ak@linux.intel.com> Cc: Bob Liu <lliubbo@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Matthew Wilcox <matthew.r.wilcox@intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/memory.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 6efe36a998ba..d8aebc52265f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2996,6 +2996,12 @@ static int do_shared_fault(struct mm_struct *mm, struct vm_area_struct *vma,
if (set_page_dirty(fault_page))
dirtied = 1;
+ /*
+ * Take a local copy of the address_space - page.mapping may be zeroed
+ * by truncate after unlock_page(). The address_space itself remains
+ * pinned by vma->vm_file's reference. We rely on unlock_page()'s
+ * release semantics to prevent the compiler from undoing this copying.
+ */
mapping = fault_page->mapping;
unlock_page(fault_page);
if ((dirtied || vma->vm_ops->page_mkwrite) && mapping) {