Skip to content

Commit

Permalink
thp: use is_zero_pfn() only after pte_present() check
Browse files Browse the repository at this point in the history
commit 47aee4d upstream.

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: ca0984c ("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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  • Loading branch information
minchank authored and gregkh committed Nov 9, 2015
1 parent 435d5d7 commit dc14f05
Showing 1 changed file with 2 additions and 1 deletion.
3 changes: 2 additions & 1 deletion mm/huge_memory.c
Original file line number Diff line number Diff line change
Expand Up @@ -2137,7 +2137,8 @@ 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 (++none_or_zero <= khugepaged_max_ptes_none)
continue;
else
Expand Down

0 comments on commit dc14f05

Please sign in to comment.