linux-kernel - Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks

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Message-ID: <20160408152801.3f0b1c33@gandalf.local.home>
Date:	Fri, 8 Apr 2016 15:28:01 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	xlpang@...hat.com, linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline
 tasks

On Fri, 8 Apr 2016 15:15:42 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From what I understand, the slowfn() modifies the task pi_list (or
> rbtree, as it is today). As this is an unlock, the task being woken
> (the next one to grab the lock) is removed from the previous task's pi
> list.
> 
> In rt_mutex_adjust_prio(current) I see it simply grabs current's
> pi_lock and calls __rt_mutex_adjust_prio(current). This calls
> rt_mutex_getprio(current) which returns current's normal prio if it
> doesn't have any pi waiters, or it looks at the top pi waiter on the
> tasks list and returns that. Which wouldn't be the task on wake_q,
> otherwise we wouldn't be deboosting in the first place.
> 

OK, I now see that the your previous patch is changing what I'm looking
at :-) This is what happens when you go away and try to catch up on
email and not read the emails by threads. I see the
rt_mutex_adjust_prio() is being changed.

I'll go back and look at your previous patch (as I looked at that while
traveling and didn't think too hard about it).

-- Steve