mm: don't overwrite mm->def_flags in do_mlockall()

With commit 8e72033f2a48 ("thp: make MADV_HUGEPAGE check for
mm->def_flags") the VM_NOHUGEPAGE flag may be set on s390 in
mm->def_flags for certain processes, to prevent future thp mappings.
This would be overwritten by do_mlockall(), which sets it back to 0 with
an optional VM_LOCKED flag set.

To fix this, instead of overwriting mm->def_flags in do_mlockall(), only
the VM_LOCKED flag should be set or cleared.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Reported-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/mm/mlock.c b/mm/mlock.c
index f0b9ce572fc7..c9bd528b01d2 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -517,11 +517,11 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 static int do_mlockall(int flags)
 {
         struct vm_area_struct * vma, * prev = NULL;
-        unsigned int def_flags = 0;
 
         if (flags & MCL_FUTURE)
-                def_flags = VM_LOCKED;
-        current->mm->def_flags = def_flags;
+                current->mm->def_flags |= VM_LOCKED;
+        else
+                current->mm->def_flags &= ~VM_LOCKED;
         if (flags == MCL_FUTURE)
                 goto out;