linux-kernel - Re: [PATCH v4 06/16] locking/rwsem: Code cleanup after files merging

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Date:   Tue, 16 Apr 2019 15:45:27 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH v4 06/16] locking/rwsem: Code cleanup after files merging

On 04/16/2019 12:17 PM, Peter Zijlstra wrote:
> On Tue, Apr 16, 2019 at 06:01:13PM +0200, Peter Zijlstra wrote:
>> @@ -794,34 +770,38 @@ static inline int __down_read_trylock(st
>>   */
>>  static inline void __down_write(struct rw_semaphore *sem)
>>  {
>> -	if (unlikely(atomic_long_cmpxchg_acquire(&sem->count, 0,
>> -						 RWSEM_WRITER_LOCKED)))
>> -		rwsem_down_write_failed(sem);
>> +	long tmp = RWSEM_UNLOCKED_VALUE;
>> +
>> +	if (unlikely(atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
>> +						     RWSEM_WRITER_LOCKED)))
> !
>
>> +		rwsem_down_write_slow(sem, TASK_UNINTERRUPTIBLE);
>>  	rwsem_set_owner(sem);
>>  }
>>  
>>  static inline int __down_write_killable(struct rw_semaphore *sem)
>>  {
>> -	if (unlikely(atomic_long_cmpxchg_acquire(&sem->count, 0,
>> -						 RWSEM_WRITER_LOCKED)))
>> -		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
>> +	long tmp = RWSEM_UNLOCKED_VALUE;
>> +
>> +	if (unlikely(atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
>> +						     RWSEM_WRITER_LOCKED))) {
> also !
>
>> +		if (IS_ERR(rwsem_down_write_slow(sem, TASK_KILLABLE)))
>>  			return -EINTR;
>> +	}
>>  	rwsem_set_owner(sem);
>>  	return 0;
>>  }
> I'm having a great day it seems, it's like back in uni, trying to find
> all the missing - signs in this page-long DE.

I am really grateful that you have spent the time to review my rwsem
patches. It is also very intense for me in the last few days
concentrating on investigating the regression and finding useful fixes
that I don't have time to deal with other stuffs.

Cheers,
Longman