From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: mm-introduce-do_shared_fault-and-drop-do_fault-fix-fix
add comment which may not be true :(
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Bob Liu <lliubbo@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 6 ++++++
1 file changed, 6 insertions(+)
diff -puN mm/memory.c~mm-introduce-do_shared_fault-and-drop-do_fault-fix-fix mm/memory.c
--- a/mm/memory.c~mm-introduce-do_shared_fault-and-drop-do_fault-fix-fix
+++ a/mm/memory.c
@@ -3009,6 +3009,12 @@ static int do_shared_fault(struct mm_str
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) {
_
--
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