linux-kernel - Re: include/linux/rtmutex.h: NOOP rt_mutex_destroy if !CONFIG_DEBUG_RT

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Date:   Fri, 2 Dec 2016 17:29:46 -0800
From:   Andy Ritger <aritger@...dia.com>
To:     Alex Goins <agoins@...dia.com>
CC:     <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
        <tglx@...utronix.de>
Subject: Re: include/linux/rtmutex.h: NOOP rt_mutex_destroy if
 !CONFIG_DEBUG_RT_MUTEXES

This seems consistent with the spirit of DEBUG_MUTEX in non-RT kernels,
so hopefully this is acceptable to the RT maintainers.

Reviewed-by: Andy Ritger <aritger@...dia.com>

Thanks,
- Andy

On Tue, Oct 25, 2016 at 07:03:51PM -0700, Alex Goins wrote:
> mutex_destroy is no-op inline when DEBUG_MUTEX is not enabled. When
> mutex_destroy is indirectly used by non-GPL kernel modules that use inline
> functions such as reservation_object_fini(), users can use a kernel with
> DEBUG_MUTEX disabled to avoid a dependence on the GPL-only symbol
> mutex_destroy.
> 
> The RT Linux patches replace mutex_destroy with rt_mutex_destroy.
> Currently, rt_mutex_destroy is GPL_ONLY irrespective of whether mutex
> debugging is enabled.
> 
> This patch aligns rt_mutex_destroy with mutex_destroy by using the same
> no-op inline technique. This allows non-GPL modules to access the same
> functionality with RT Linux as with regular Linux.
> 
> Signed-off-by: Alex Goins <agoins@...dia.com>
> ---
>  include/linux/rtmutex.h  | 7 ++++++-
>  kernel/locking/rtmutex.c | 5 ++---
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
> index 1abba5c..741e844 100644
> --- a/include/linux/rtmutex.h
> +++ b/include/linux/rtmutex.h
> @@ -56,6 +56,12 @@ struct hrtimer_sleeper;
>  #endif
>  
>  #ifdef CONFIG_DEBUG_RT_MUTEXES
> + extern void rt_mutex_destroy(struct rt_mutex *lock);
> +#else
> + static inline void rt_mutex_destroy(struct rt_mutex *lock) {}
> +#endif
> +
> +#ifdef CONFIG_DEBUG_RT_MUTEXES
>  # define __DEBUG_RT_MUTEX_INITIALIZER(mutexname) \
>  	, .name = #mutexname, .file = __FILE__, .line = __LINE__
>  # define rt_mutex_init(mutex)			__rt_mutex_init(mutex, __func__)
> @@ -87,7 +93,6 @@ static inline int rt_mutex_is_locked(struct rt_mutex *lock)
>  }
>  
>  extern void __rt_mutex_init(struct rt_mutex *lock, const char *name);
> -extern void rt_mutex_destroy(struct rt_mutex *lock);
>  
>  extern void rt_mutex_lock(struct rt_mutex *lock);
>  extern int rt_mutex_lock_interruptible(struct rt_mutex *lock);
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 1ec0f48..8d3a80e 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -1513,6 +1513,7 @@ bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
>  	return rt_mutex_slowunlock(lock, wqh);
>  }
>  
> +#ifdef CONFIG_DEBUG_RT_MUTEXES
>  /**
>   * rt_mutex_destroy - mark a mutex unusable
>   * @lock: the mutex to be destroyed
> @@ -1524,12 +1525,10 @@ bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
>  void rt_mutex_destroy(struct rt_mutex *lock)
>  {
>  	WARN_ON(rt_mutex_is_locked(lock));
> -#ifdef CONFIG_DEBUG_RT_MUTEXES
>  	lock->magic = NULL;
> -#endif
>  }
> -
>  EXPORT_SYMBOL_GPL(rt_mutex_destroy);
> +#endif
>  
>  /**
>   * __rt_mutex_init - initialize the rt lock