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

Peter Zijlstra
2021-03-17T17:41:39Z

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)