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

Peter Zijlstra
2021-03-17T17:46:37Z

On Wed, Mar 17, 2021 at 06:40:27PM +0100, 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, \

,name = #class "_mutex", \

and it 'works', but shees!

> + .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)