kmemleak: clear stale pointers from task stacks

Kmemleak considers any pointers on task stacks as references.  This
patch clears newly allocated and reused vmap stacks.

Link: http://lkml.kernel.org/r/150728990124.744199.8403409836394318684.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index e702cb9ffbd8..07cc743698d3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -215,6 +215,10 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
                 if (!s)
                         continue;
 
+#ifdef CONFIG_DEBUG_KMEMLEAK
+                /* Clear stale pointers from reused stack. */
+                memset(s->addr, 0, THREAD_SIZE);
+#endif
                 tsk->stack_vm_area = s;
                 return s->addr;
         }