linux-kernel - Re: [PATCH RT] arm64: fpsimd: use a local_lock() in addition to local_bh

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Date:   Wed, 11 Jul 2018 09:25:55 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RT] arm64: fpsimd: use a local_lock() in addition to
 local_bh_disable()

On Tue, 22 May 2018 19:33:33 +0200
Sebastian Andrzej Siewior <bigeasy@...utronix.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@...utronix.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@...utronix.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