linux-kernel - Re: [PATCH v3 1/6] rtmutex: Deboost before waking up the top waiter

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Date:	Mon, 18 Apr 2016 17:41:45 +0800
From:	Xunlei Pang <xpang@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v3 1/6] rtmutex: Deboost before waking up the top waiter

On 2016/04/18 at 17:02, Thomas Gleixner wrote:
> On Mon, 18 Apr 2016, Xunlei Pang wrote:
>> On 2016/04/18 at 16:23, Thomas Gleixner wrote:
>>> On Thu, 14 Apr 2016, Xunlei Pang wrote:
>>>> We should deboost before waking the high-prio task such that
>>>> we don't run two tasks with the 'same' priority.
>>> No. This is fundamentaly broken.
>>>  
>>> T1 (prio 0)	lock(X)
>>>
>>> -->	 	preemption
>>>
>>> T2 (prio 10)	lock(X)
>>>    	 	boost(T1)
>>> 		schedule()
>>>
>>> T1 (prio 10)	unlock(X)
>> We add a preempt_disable() before deboost to avoid the breakage,
>> there's also some comment about this in the patch's code.
> So the changelog is useless and misleading. Neither does it explain what's
> wrong with having two tasks with the same priority in running state.

Sorry about that, will improve it.

Regards,
Xunlei

>
> Thanks,
>
> 	tglx
>
>
>
>