linux-kernel - Re: [PATCH v3 5/6] sched/deadline/rtmutex: Fix unprotected PI access in enqueue_task

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Message-ID: <20160420122552.GY3430@twins.programming.kicks-ass.net>
Date:	Wed, 20 Apr 2016 14:25:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	xlpang@...hat.com
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Juri Lelli <juri.lelli@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v3 5/6] sched/deadline/rtmutex: Fix unprotected PI access
 in enqueue_task_dl()

On Fri, Apr 15, 2016 at 10:19:12AM +0800, Xunlei Pang wrote:
> On 2016/04/15 at 09:58, Xunlei Pang wrote:
> > On 2016/04/14 at 23:31, Peter Zijlstra wrote:
> >> On Thu, Apr 14, 2016 at 07:37:06PM +0800, Xunlei Pang wrote:
> >>> We access @pi_task's data without any lock in enqueue_task_dl(), though
> >>> checked "dl_prio(pi_task->normal_prio)" condition, that's not enough.
> >> The proper fix is to ensure that pi_task is guaranteed to be blocked.
> > Even if pi_task was blocked, its parameters are still allowed to be changed,
> > so we have to do that. Did I miss something?
> >
> > Regards,
> > Xunlei
> 
> Fortunately, I just reproduced through an overnight test, so it really happened in reality as I thought.

But what happens? How is it changed when it is blocked?