[PATCH RESEND v1] locking/ww_mutex: Prevent read of uninitialized memory

[PATCH RESEND v1] locking/ww_mutex: Prevent read of uninitialized memory

[Robert Foss]

On "missed ABBA deadlock" abba.result is read, but not initialized
in all situations.

Detected by CoverityScan, CID#1402035 ("Uninitialized scalar variable")

Signed-off-by: Robert Foss <robert.foss@collabora.com>
---
 kernel/locking/test-ww_mutex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 6b7abb334ca6..beb76693ccfa 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -196,7 +196,7 @@ static void test_abba_work(struct work_struct *work)
 
 static int test_abba(bool resolve)
 {
-	struct test_abba abba;
+	struct test_abba abba = { 0 };
 	struct ww_acquire_ctx ctx;
 	int err, ret;
 
-- 
2.11.0.453.g787f75f05

Re: [PATCH RESEND v1] locking/ww_mutex: Prevent read of uninitialized memory

[Chris Wilson]

On Tue, Mar 14, 2017 at 03:44:02PM -0400, Robert Foss wrote:
> On "missed ABBA deadlock" abba.result is read, but not initialized
> in all situations.
> 
> Detected by CoverityScan, CID#1402035 ("Uninitialized scalar variable")

It's unconditionally set by the worker, and only accessed by the parent
after the flush_work() barrier.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

Re: [PATCH RESEND v1] locking/ww_mutex: Prevent read of uninitialized memory

[kbuild test robot]

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Hi Robert,

[auto build test WARNING on tip/locking/core]
[also build test WARNING on v4.11-rc2 next-20170310]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Robert-Foss/locking-ww_mutex-Prevent-read-of-uninitialized-memory/20170317-085627
config: x86_64-randconfig-i0-201711 (attached as .config)
compiler: gcc-4.9 (Debian 4.9.4-2) 4.9.4
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   kernel/locking/test-ww_mutex.c: In function 'test_abba':
>> kernel/locking/test-ww_mutex.c:199:9: warning: missing braces around initializer [-Wmissing-braces]
     struct test_abba abba = { 0 };
            ^
   kernel/locking/test-ww_mutex.c:199:9: warning: (near initialization for 'abba.work') [-Wmissing-braces]

vim +199 kernel/locking/test-ww_mutex.c

   183		if (abba->resolve && err == -EDEADLK) {
   184			ww_mutex_unlock(&abba->b_mutex);
   185			ww_mutex_lock_slow(&abba->a_mutex, &ctx);
   186			err = ww_mutex_lock(&abba->b_mutex, &ctx);
   187		}
   188	
   189		if (!err)
   190			ww_mutex_unlock(&abba->a_mutex);
   191		ww_mutex_unlock(&abba->b_mutex);
   192		ww_acquire_fini(&ctx);
   193	
   194		abba->result = err;
   195	}
   196	
   197	static int test_abba(bool resolve)
   198	{
 > 199		struct test_abba abba = { 0 };
   200		struct ww_acquire_ctx ctx;
   201		int err, ret;
   202	
   203		ww_mutex_init(&abba.a_mutex, &ww_class);
   204		ww_mutex_init(&abba.b_mutex, &ww_class);
   205		INIT_WORK_ONSTACK(&abba.work, test_abba_work);
   206		init_completion(&abba.a_ready);
   207		init_completion(&abba.b_ready);

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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