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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>
This commit is contained in:
Hugh Dickins 2014-08-06 16:05:08 -07:00 committed by Linus Torvalds
parent 474750aba8
commit c0d73261f5
1 changed files with 1 additions and 1 deletions
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2
mm/memory.c
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@ -3181,7 +3181,7 @@ static int handle_pte_fault(struct mm_struct *mm,
pte_t entry; pte_t entry;
spinlock_t *ptl; spinlock_t *ptl;
entry = *pte; entry = ACCESS_ONCE(*pte);
if (!pte_present(entry)) { if (!pte_present(entry)) {
if (pte_none(entry)) { if (pte_none(entry)) {
if (vma->vm_ops) { if (vma->vm_ops) {