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

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Message-ID: <6a1d2610-2407-4449-a3ff-2fbfa85f96ae@linux.dev>
Date: Tue, 24 Jun 2025 09:35:15 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
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, mingo@...hat.com,
 mingzhe.yang@...com, peterz@...radead.org, rostedt@...dmis.org,
 senozhatsky@...omium.org, tfiga@...omium.org, will@...nel.org,
 Lance Yang <ioworker0@...il.com>
Subject: Re: [PATCH RFC 1/3] locking/rwsem: make owner helpers globally
 available



On 2025/6/24 08:17, Masami Hiramatsu (Google) wrote:
> 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!

Thanks for taking the time to review!
Lance

> 
>> 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
>>
> 
>