hugepage_vma_revalidate() tries to re-check if we still should try to collapse small pages into huge one after the re-acquiring mmap_sem. The problem Dmitry Vyukov reported[1] is that the vma found by hugepage_vma_revalidate() can be suitable for huge pages, but not the same vma we had before dropping mmap_sem. And dereferencing original vma can lead to fun results.. Let's use vma hugepage_vma_revalidate() found instead of assuming it's the same as what we had before the lock was dropped. [1] http://lkml.kernel.org/r/CACT4Y+Z3gigBvhca9kRJFcjX0G70V_nRhbwKBU+yGoESBDKi9Q@mail.gmail.com Link: http://lkml.kernel.org/r/20160907122559.GA6542@black.fi.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reported-by: Dmitry Vyukov <dvyukov@google.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Vegard Nossum <vegard.nossum@oracle.com> Cc: Sasha Levin <levinsasha928@gmail.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Greg Thelen <gthelen@google.com> Cc: Suleiman Souhlal <suleiman@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: David Rientjes <rientjes@google.com> Cc: syzkaller <syzkaller@googlegroups.com> Cc: Kostya Serebryany <kcc@google.com> Cc: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>