linux-kernel - Re: [PATCH RT v3] arm64: fpsimd: use preemp_disable in addition to local_bh

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Date:   Fri, 27 Jul 2018 09:56:44 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mike Galbraith <efault@....de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Dave Martin <Dave.Martin@....com>,
        linux-rt-users@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RT v3] arm64: fpsimd: use preemp_disable in addition to
 local_bh_disable()

On 2018-07-27 05:17:23 [+0200], Mike Galbraith wrote:
> On Thu, 2018-07-26 at 17:06 +0200, Sebastian Andrzej Siewior wrote:
> > 
> > @@ -1115,6 +1139,7 @@ void kernel_neon_begin(void)
> >  
> >  	BUG_ON(!may_use_simd());
> >  
> > +	preempt_disable();
> >  	local_bh_disable();
> >  
> >  	__this_cpu_write(kernel_neon_busy, true);
> > @@ -1131,6 +1156,7 @@ void kernel_neon_begin(void)
> >  	preempt_disable();
> 
> Nit: this preempt_disable() could be removed...
>  
> >  	local_bh_enable();
> > +	preempt_enable();
> >  }
> >  EXPORT_SYMBOL(kernel_neon_begin);
> 
> ...instead of adding this one.

It could. I have currently no idea for the long term solution and this
keeps track what is intended to do. It might get replaced with
preempt_.*_rt()…

> 	-Mike

Sebastian