Re: [tip: locking/urgent] locking/ww_mutex: Treat ww_mutex_lock() like a trylock

[Waiman Long]

On 3/17/21 1:40 PM, Peter Zijlstra wrote:
On Wed, Mar 17, 2021 at 05:48:48PM +0100, Peter Zijlstra wrote:
I think you'll find that if you use ww_mutex_init() it'll all work. Let
me go and zap this patch, and then I'll try and figure out why
DEFINE_WW_MUTEX() is buggered.
Moo, I can't get the compiler to do as I want :/

The below is so close but doesn't actually compile.. Maybe we should
just give up on DEFINE_WW_MUTEX and simply remove it.

---
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 0cd631a19727..85f50538f26a 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -129,12 +129,15 @@ do {                                                      
                \
  # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
  #endif
  
-#define __MUTEX_INITIALIZER(lockname) \
+#define ___MUTEX_INITIALIZER(lockname, depmap) \
                { .owner = ATOMIC_LONG_INIT(0) \
                , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
                , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
                __DEBUG_MUTEX_INITIALIZER(lockname) \
-               __DEP_MAP_MUTEX_INITIALIZER(lockname) }
+               depmap }
+
+#define __MUTEX_INITIALIZER(lockname) \
+               ___MUTEX_INITIALIZER(lockname, 
__DEP_MAP_MUTEX_INITIALIZER(lockname))
  
  #define DEFINE_MUTEX(mutexname) \
        struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 6ecf2a0220db..c62a030652b4 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -50,9 +50,17 @@ struct ww_acquire_ctx {
  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  # define __WW_CLASS_MUTEX_INITIALIZER(lockname, class) \
-               , .ww_class = class
+               , .ww_class = &(class)
+
+# define __DEP_MAP_WW_MUTEX_INITIALIZER(lockname, class) \
+               , .dep_map = { \
+                       .key = &(class).mutex_key, \
+                       .name = (class).mutex_name, \
+                       .wait_type_inner = LD_WAIT_SLEEP, \
+               }
  #else
  # define __WW_CLASS_MUTEX_INITIALIZER(lockname, class)
+# define __DEP_MAP_WW_MUTEX_INITIALIZER(lockname, class)
  #endif
  
  #define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die)	    \
@@ -62,7 +70,8 @@ struct ww_acquire_ctx {
                , .is_wait_die = _is_wait_die }
  
  #define __WW_MUTEX_INITIALIZER(lockname, class) \
-               { .base =  __MUTEX_INITIALIZER(lockname.base) \
+               { .base =  ___MUTEX_INITIALIZER(lockname.base, \
+                       __DEP_MAP_WW_MUTEX_INITIALIZER(lockname.base, class)) \
                __WW_CLASS_MUTEX_INITIALIZER(lockname, class) }
  
  #define DEFINE_WD_CLASS(classname) \
diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 0ab94e1f1276..e8305233eb0b 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -358,9 +358,9 @@ static struct lock_torture_ops mutex_lock_ops = {
  
  #include <linux/ww_mutex.h>
  static DEFINE_WD_CLASS(torture_ww_class);
-static DEFINE_WW_MUTEX(torture_ww_mutex_0, &torture_ww_class);
-static DEFINE_WW_MUTEX(torture_ww_mutex_1, &torture_ww_class);
-static DEFINE_WW_MUTEX(torture_ww_mutex_2, &torture_ww_class);
+static DEFINE_WW_MUTEX(torture_ww_mutex_0, torture_ww_class);
+static DEFINE_WW_MUTEX(torture_ww_mutex_1, torture_ww_class);
+static DEFINE_WW_MUTEX(torture_ww_mutex_2, torture_ww_class);
  
  static int torture_ww_mutex_lock(void)
  __acquires(torture_ww_mutex_0)

I changed locktorture to use ww_mutex_init() and the lockdep splat was 
indeed gone. So zapping WW_MUTEX_INIT() and use ww_mutex_init() is a 
possible solution. I will send out a patch to do that.

Thanks,
Longman