linux-kernel - Re: [PATCH 3/8] sched/wait: Use __add_wait_queue{_tail}

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Date:	Wed, 16 Apr 2014 18:51:51 +0900
From:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	<rostedt@...dmis.org>, <fweisbec@...il.com>, <mingo@...hat.com>,
	<acme@...stprotocols.net>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/8] sched/wait: Use __add_wait_queue{_tail}_exclusive()
 as possible.

On 04/15/2014 10:49 PM, Peter Zijlstra wrote:
> On Tue, Apr 15, 2014 at 09:32:52PM +0900, Dongsheng Yang wrote:
>> From: Dongsheng <yangds.fnst@...fujitsu.com>
>>
>> There is already a function in include/linux/wait.h to cover the
>> 'exclusive' usage. So we can use it in sched/wait.c to replace
>> the opened implementation of it.
>>
>> Signed-off-by: Dongsheng <yangds.fnst@...fujitsu.com>
>> ---
>>   kernel/sched/wait.c | 6 ++----
>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
>> index 283750e..b04827e 100644
>> --- a/kernel/sched/wait.c
>> +++ b/kernel/sched/wait.c
>> @@ -38,9 +38,8 @@ void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
>>   	unsigned long flags;
>>   
>>   	trace_sched_wait(current);
>> -	wait->flags |= WQ_FLAG_EXCLUSIVE;
>>   	spin_lock_irqsave(&q->lock, flags);
>> -	__add_wait_queue_tail(q, wait);
>> +	__add_wait_queue_tail_exclusive(q, wait);
>>   	spin_unlock_irqrestore(&q->lock, flags);
>>   }
>>   EXPORT_SYMBOL(add_wait_queue_exclusive);
>> @@ -192,10 +191,9 @@ prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
>>   	unsigned long flags;
>>   
>>   	trace_sched_wait(current);
>> -	wait->flags |= WQ_FLAG_EXCLUSIVE;
>>   	spin_lock_irqsave(&q->lock, flags);
>>   	if (list_empty(&wait->task_list))
>> -		__add_wait_queue_tail(q, wait);
>> +		__add_wait_queue_tail_exclusive(q, wait);
>>   	set_current_state(state);
>>   	spin_unlock_irqrestore(&q->lock, flags);
> That is not a no-op, if !list_empty() we loose the WQ_flag

Oh, yes, my mistake. Thanx
> .
>

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