linux-kernel - Re: [PATCH 4/3] rtmutex: Avoid barrier in rt_mutex_handle

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Message-ID: <20160322122050.GM6344@twins.programming.kicks-ass.net>
Date:	Tue, 22 Mar 2016 13:20:50 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Davidlohr Bueso <dave@...olabs.net>, tglx@...utronix.de,
	mingo@...nel.org, bigeasy@...utronix.de, umgwanakikbuti@...il.com,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	kmo@...erainc.com
Subject: Re: [PATCH 4/3] rtmutex: Avoid barrier in rt_mutex_handle_deadlock

On Tue, Mar 22, 2016 at 12:32:21PM +0100, Heiko Carstens wrote:
> On Tue, Mar 22, 2016 at 11:21:53AM +0100, Peter Zijlstra wrote:

> > And s390 does something entirely vile, no idea what.
> 
> For the two s390 usages tsk equals current. So it could be easily replaced
> with set_current_state().

Hmm indeed, I only saw tsk = find_task_by_pid_ns() and didn't look
further, but you do indeed have an assertion later that ensures task ==
current.

I still don't get that code though; why would you set the current task
state to UNINTERRUPTIBLE, also set need_resched, but then not call
schedule() at all.

Clearly something magical is going on and its not clear.