linux-kernel - Re: [PATCH RT] Align rt_mutex inlining with upstream behavior

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Message-ID: <20170211175241.GA30998@gmail.com>
Date:   Sat, 11 Feb 2017 18:52:42 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Ritger <aritger@...dia.com>, Alex Goins <agoins@...dia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH RT] Align rt_mutex inlining with upstream behavior


* Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> On 2017-02-10 10:09:29 [-0800], Andy Ritger wrote:
> > Is the
> > 
> >     WARN_ON(rt_mutex_is_locked(lock));
> > 
> > in rt_mutex_destroy() valuable in non-CONFIG_DEBUG_MUTEXES kernels,
> > such that it would be better to always call it, and not noop away mutex_destroy()
> > non-CONFIG_DEBUG_MUTEXES kernels?  I thought that was your objection to
> > Alex's original patch.
> 
> It kind of was…
> So first I removed the GPL symbol. Then I wasn't too happy about it
> especially since it was not introduced as part of RT. So I reverted that
> changed and aligned with mainline behaviour (the mutex_rt.h hunk). But
> then I noticed that with CONFIG_DEBUG_MUTEXES=n and
> CONFIG_DEBUG_RT_MUTEXES=y we still have a regression compared to !RT and
> this was the initial motivation to fix things.
> Then I got curious why mutex_lock() (which is essential rt_mutex_lock())
> works and noticed the wrapper around it. And while looking at it I
> decided to go back to strip the GPL part from export symbol instead of
> adding a wrapper. And here I am.
> Then I was looking at the patch and decided to align with mainline (and
> keep that one hunk) in case Ingo ask for his GPL symbol.

tglx and Peter Zijlstra are main co-authors of kernel/locking/rtmutex.c, and every 
author (copyright holder) has to agree to changing a GPL export of a kernel 
subsystem's API to a non-GPL export.

Thanks,

	Ingo