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>

2 files changed, 5 insertions, 1 deletions

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 905d769d8ddc..5f7eeab990fe 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -42,7 +42,7 @@ enum {
 #define THREAD_ALIGN    THREAD_SIZE
 #endif
 
-#ifdef CONFIG_DEBUG_STACK_USAGE
+#if IS_ENABLED(CONFIG_DEBUG_STACK_USAGE) || IS_ENABLED(CONFIG_DEBUG_KMEMLEAK)
 # define THREADINFO_GFP         (GFP_KERNEL_ACCOUNT | __GFP_NOTRACK | \
                                  __GFP_ZERO)
 #else
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;
         }