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| author | Hugh Dickins <hughd@google.com> | 2014-08-06 16:05:08 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-08-06 18:01:15 -0700 |
| commit | c0d73261f5c1355a35b8b40e871d31578ce0c044 (patch) | |
| tree | 9612726cd85eab1bb6f89dcf5c8dd49c532cc572 /mm/memory.c | |
| parent | 474750aba88817c53f39424e5567b8e4acc4b39b (diff) | |
| download | lwn-c0d73261f5c1355a35b8b40e871d31578ce0c044.tar.gz lwn-c0d73261f5c1355a35b8b40e871d31578ce0c044.zip | |
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.c | 2 |
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) { |