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authorMinchan Kim <minchan@kernel.org>2015-10-22 13:32:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-10-23 17:55:10 +0900
commit47aee4d8e314384807e98b67ade07f6da476aa75 (patch)
parentb8fa0efa01109e294e9be610465c324f771cb5ba (diff)
thp: use is_zero_pfn() only after pte_present() check
Use is_zero_pfn() on pteval only after pte_present() check on pteval (It might be better idea to introduce is_zero_pte() which checks pte_present() first). Otherwise when working on a swap or migration entry and if pte_pfn's result is equal to zero_pfn by chance, we lose user's data in __collapse_huge_page_copy(). So if you're unlucky, the application segfaults and finally you could see below message on exit: BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3 Fixes: ca0984caa823 ("mm: incorporate zero pages into transparent huge pages") Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Cc: <stable@vger.kernel.org> [4.1+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4b06b8db9df2..bbac913f96bc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2206,7 +2206,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
- if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ if (pte_none(pteval) || (pte_present(pteval) &&
+ is_zero_pfn(pte_pfn(pteval)))) {
if (!userfaultfd_armed(vma) &&
++none_or_zero <= khugepaged_max_ptes_none)