linux-kernel - Re: [PATCH 2/2] locking/mutex: Use mutex flags macro instead of hard code value

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Date:   Tue, 30 Jul 2019 21:55:38 +0530
From:   Mukesh Ojha <mojha@...eaurora.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, will@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] locking/mutex: Use mutex flags macro instead of hard
 code value


On 7/30/2019 9:32 PM, Peter Zijlstra wrote:
> On Tue, Jul 30, 2019 at 06:10:49PM +0530, Mukesh Ojha wrote:
>
>> To make it static , i have to export mutex_is_locked() after moving it
>> inside mutex.c, so that other module can use it.
> Yep, see below -- completely untested.
>
>> Also are we thinking of removing
>> static inline /* __deprecated */ __must_check enum
>> mutex_trylock_recursive_enum
>> mutex_trylock_recursive(struct mutex *lock)
>>
>> inside linux/mutex.h in future ?
>>
>> As i see it is used at one or two places and there is a check inside
>> checkpatch guarding its further use .
> That was the idea; recursive locking is evil, but we have these two
> legacy sites.
>
> ---
>
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index dcd03fee6e01..eb8c62aba263 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -65,29 +65,6 @@ struct mutex {
>   #endif
>   };
>   
> -/*
> - * Internal helper function; C doesn't allow us to hide it :/
> - *
> - * DO NOT USE (outside of mutex code).
> - */
> -static inline struct task_struct *__mutex_owner(struct mutex *lock)
> -{
> -	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x07);
> -}
> -
> -/*
> - * This is the control structure for tasks blocked on mutex,
> - * which resides on the blocked task's kernel stack:
> - */
> -struct mutex_waiter {
> -	struct list_head	list;
> -	struct task_struct	*task;
> -	struct ww_acquire_ctx	*ww_ctx;
> -#ifdef CONFIG_DEBUG_MUTEXES
> -	void			*magic;
> -#endif
> -};
> -
>   #ifdef CONFIG_DEBUG_MUTEXES
>   
>   #define __DEBUG_MUTEX_INITIALIZER(lockname)				\
> @@ -144,10 +121,7 @@ extern void __mutex_init(struct mutex *lock, const char *name,
>    *
>    * Returns true if the mutex is locked, false if unlocked.
>    */
> -static inline bool mutex_is_locked(struct mutex *lock)
> -{
> -	return __mutex_owner(lock) != NULL;
> -}
> +extern bool mutex_is_locked(struct mutex *lock);
>   
>   /*
>    * See kernel/locking/mutex.c for detailed documentation of these APIs.
> @@ -220,13 +194,7 @@ enum mutex_trylock_recursive_enum {
>    *  - MUTEX_TRYLOCK_SUCCESS   - lock acquired,
>    *  - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
>    */
> -static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
> -mutex_trylock_recursive(struct mutex *lock)
> -{
> -	if (unlikely(__mutex_owner(lock) == current))
> -		return MUTEX_TRYLOCK_RECURSIVE;
> -
> -	return mutex_trylock(lock);
> -}
> +extern /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
> +mutex_trylock_recursive(struct mutex *lock);
>   
>   #endif /* __LINUX_MUTEX_H */
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index 5e069734363c..2f73935a6053 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -36,6 +36,19 @@
>   # include "mutex.h"
>   #endif
>   
> +/*
> + * This is the control structure for tasks blocked on mutex,
> + * which resides on the blocked task's kernel stack:
> + */
> +struct mutex_waiter {
> +	struct list_head	list;
> +	struct task_struct	*task;
> +	struct ww_acquire_ctx	*ww_ctx;
> +#ifdef CONFIG_DEBUG_MUTEXES
> +	void			*magic;
> +#endif
> +};

i already did in v2  except this above waiter struct, will do it in v3.

Cheers,

Mukesh

> +
>   void
>   __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
>   {
> @@ -65,6 +78,16 @@ EXPORT_SYMBOL(__mutex_init);
>   
>   #define MUTEX_FLAGS		0x07
>   
> +/*
> + * Internal helper function; C doesn't allow us to hide it :/
> + *
> + * DO NOT USE (outside of mutex code).
> + */
> +static inline struct task_struct *__mutex_owner(struct mutex *lock)
> +{
> +	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
> +}
> +
>   static inline struct task_struct *__owner_task(unsigned long owner)
>   {
>   	return (struct task_struct *)(owner & ~MUTEX_FLAGS);
> @@ -75,6 +98,22 @@ static inline unsigned long __owner_flags(unsigned long owner)
>   	return owner & MUTEX_FLAGS;
>   }
>   
> +bool mutex_is_locked(struct mutex *lock)
> +{
> +	return __mutex_owner(lock) != NULL;
> +}
> +EXPORT_SYMBOL(mutex_is_locked);
> +
> +__must_check enum mutex_trylock_recursive_enum
> +mutex_trylock_recursive(struct mutex *lock)
> +{
> +	if (unlikely(__mutex_owner(lock) == current))
> +		return MUTEX_TRYLOCK_RECURSIVE;
> +
> +	return mutex_trylock(lock);
> +}
> +EXPORT_SYMBOL(mutex_trylock_recursive);
> +
>   /*
>    * Trylock variant that retuns the owning task on failure.
>    */