From mboxrd@z Thu Jan  1 00:00:00 1970
From: rostedt@goodmis.org (Steven Rostedt)
Date: Wed, 11 Jul 2018 09:25:55 -0400
Subject: [PATCH RT] arm64: fpsimd: use a local_lock() in addition to
 local_bh_disable()
In-Reply-To: <20180522173333.aawadhkcekzvrswp@linutronix.de>
References: <20180517124006.ohygrrpg7z2moqqt@linutronix.de>
 <20180522131004.3012953c@gandalf.local.home>
 <20180522172115.fpqguqlsq6bavtxy@linutronix.de>
 <20180522132429.6f1dcf92@gandalf.local.home>
 <20180522173333.aawadhkcekzvrswp@linutronix.de>
Message-ID: <20180711092555.268adf7f@gandalf.local.home>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, 22 May 2018 19:33:33 +0200
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> On 2018-05-22 13:24:29 [-0400], Steven Rostedt wrote:
> > On Tue, 22 May 2018 19:21:16 +0200
> > Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> >   
> > > On 2018-05-22 13:10:04 [-0400], Steven Rostedt wrote:  
> > > > On Thu, 17 May 2018 14:40:06 +0200
> > > > Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> > > >     
> > > > > +static DEFINE_LOCAL_IRQ_LOCK(fpsimd_lock);
> > > > >  /*
> > > > >   * Update current's FPSIMD/SVE registers from thread_struct.
> > > > >   *
> > > > > @@ -594,6 +595,7 @@ int sve_set_vector_length(struct task_struct *task,
> > > > >  	 * non-SVE thread.
> > > > >  	 */
> > > > >  	if (task == current) {
> > > > > +		local_lock(fpsimd_lock);
> > > > >  		local_bh_disable();    
> > > > 
> > > > I'm surprised that we don't have a "local_lock_bh()"?    
> > > 
> > > right. Like the last time when we introduced a global lock with no
> > > locking context? 
> > >   
> > 
> > I meant, we could have local_lock_bh(fpsimd_lock); that would turn into
> > a local_bh_disable() when !PREEMPT_RT.  
> 
> Oh that part. That could be possible I guess. I need to look into the
> second part which disables preemption while the FPU is taken.
>

Did you decide to create a local_lock_bh(lock) function? I don't see it.

And should this be backported to 4.14-rt too? You state you saw this in
4.16-rt, but did you start doing something different then, or did the
kernel change?

Thanks!

-- Steve