linux-kernel - Re: [PATCH RFC 1/3] locking/rwsem: make owner helpers globally available

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Message-Id: <20250624091731.f4d3cf296943ce45e97a631f@kernel.org>
Date: Tue, 24 Jun 2025 09:17:31 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Lance Yang <ioworker0@...il.com>
Cc: akpm@...ux-foundation.org, zi.li@...ux.dev, anna.schumaker@...cle.com,
 boqun.feng@...il.com, joel.granados@...nel.org, jstultz@...gle.com,
 kent.overstreet@...ux.dev, leonylgao@...cent.com,
 linux-kernel@...r.kernel.org, longman@...hat.com, mhiramat@...nel.org,
 mingo@...hat.com, mingzhe.yang@...com, peterz@...radead.org,
 rostedt@...dmis.org, senozhatsky@...omium.org, tfiga@...omium.org,
 will@...nel.org, Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH RFC 1/3] locking/rwsem: make owner helpers globally
 available

On Thu, 12 Jun 2025 12:19:24 +0800
Lance Yang <ioworker0@...il.com> wrote:

> From: Lance Yang <lance.yang@...ux.dev>
> 
> In preparation for extending blocker tracking to support rwsems, make the
> rwsem_owner() and is_rwsem_reader_owned() helpers globally available for
> determining if the blocker is a writer or one of the readers.
> 

Looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thanks!

> Signed-off-by: Lance Yang <lance.yang@...ux.dev>
> ---
>  include/linux/rwsem.h  | 12 ++++++++++++
>  kernel/locking/rwsem.c |  8 +++++---
>  2 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> index c8b543d428b0..544853bed5b9 100644
> --- a/include/linux/rwsem.h
> +++ b/include/linux/rwsem.h
> @@ -132,6 +132,18 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
>  	return !list_empty(&sem->wait_list);
>  }
>  
> +#if defined(CONFIG_DEBUG_RWSEMS) || defined(CONFIG_DETECT_HUNG_TASK_BLOCKER)
> +/*
> + * Return just the real task structure pointer of the owner
> + */
> +extern struct task_struct *rwsem_owner(struct rw_semaphore *sem);
> +
> +/*
> + * Return true if the rwsem is owned by a reader.
> + */
> +extern bool is_rwsem_reader_owned(struct rw_semaphore *sem);
> +#endif
> +
>  #else /* !CONFIG_PREEMPT_RT */
>  
>  #include <linux/rwbase_rt.h>
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 2ddb827e3bea..6cb29442d4fc 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -181,11 +181,11 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
>  	__rwsem_set_reader_owned(sem, current);
>  }
>  
> -#ifdef CONFIG_DEBUG_RWSEMS
> +#if defined(CONFIG_DEBUG_RWSEMS) || defined(CONFIG_DETECT_HUNG_TASK_BLOCKER)
>  /*
>   * Return just the real task structure pointer of the owner
>   */
> -static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
> +struct task_struct *rwsem_owner(struct rw_semaphore *sem)
>  {
>  	return (struct task_struct *)
>  		(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
> @@ -194,7 +194,7 @@ static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
>  /*
>   * Return true if the rwsem is owned by a reader.
>   */
> -static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
> +bool is_rwsem_reader_owned(struct rw_semaphore *sem)
>  {
>  	/*
>  	 * Check the count to see if it is write-locked.
> @@ -205,7 +205,9 @@ static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
>  		return false;
>  	return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
>  }
> +#endif
>  
> +#ifdef CONFIG_DEBUG_RWSEMS
>  /*
>   * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
>   * is a task pointer in owner of a reader-owned rwsem, it will be the
> -- 
> 2.49.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>