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authorHugh Dickins <hughd@google.com>2014-08-07 03:05:08 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-07 05:01:15 +0400
commitc0d73261f5c1355a35b8b40e871d31578ce0c044 (patch)
tree9612726cd85eab1bb6f89dcf5c8dd49c532cc572 /mm/memory.c
parent474750aba88817c53f39424e5567b8e4acc4b39b (diff)
downloadlinux-c0d73261f5c1355a35b8b40e871d31578ce0c044.tar.xz
mm/memory.c: use entry = ACCESS_ONCE(*pte) in handle_pte_fault()
Use ACCESS_ONCE() in handle_pte_fault() when getting the entry or orig_pte upon which all subsequent decisions and pte_same() tests will be made. I have no evidence that its lack is responsible for the mm/filemap.c:202 BUG_ON(page_mapped(page)) in __delete_from_page_cache() found by trinity, and I am not optimistic that it will fix it. But I have found no other explanation, and ACCESS_ONCE() here will surely not hurt. If gcc does re-access the pte before passing it down, then that would be disastrous for correct page fault handling, and certainly could explain the page_mapped() BUGs seen (concurrent fault causing page to be mapped in a second time on top of itself: mapcount 2 for a single pte). Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 8b44f765b645..06ff0720d75a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3181,7 +3181,7 @@ static int handle_pte_fault(struct mm_struct *mm,
pte_t entry;
spinlock_t *ptl;
- entry = *pte;
+ entry = ACCESS_ONCE(*pte);
if (!pte_present(entry)) {
if (pte_none(entry)) {
if (vma->vm_ops) {