linux-kernel - Re: [PATCH] ARM: remove redundant irq disable at halt and restart

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Date:	Fri, 24 Oct 2014 21:28:45 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Felipe Balbi <balbi@...com>
Cc:	Johan Hovold <johan@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: remove redundant irq disable at halt and restart

On Fri, Oct 24, 2014 at 02:21:11PM -0500, Felipe Balbi wrote:
> On Fri, Oct 24, 2014 at 02:16:27PM -0500, Felipe Balbi wrote:
> > On Fri, Oct 24, 2014 at 09:06:32PM +0200, Johan Hovold wrote:
> > > Remove redundant local_irq_disable() at machine halt and restart.
> > > 
> > > Since commit 44424c34049f ("ARM: 7803/1: Fix deadlock scenario with
> > > smp_send_stop()") interrupts are disabled before stopping secondary
> > > CPUs.
> > 
> > Assuming this is correct, you should have:
> > 
> > Fixes: 44424c3 (ARM: 7803/1: Fix deadlock scenario with smp_send_stop())
> > Cc: <stable@...r.kernel.org> # v3.12+

It's not a bug. Just a redundant disabling of already disabled
interrupts, something which could possibly lead someone to believe that
interrupts could be re-enabled by the power-off handler.

And if that was the case, wouldn't that introduce the bug that
44424c34049f ("ARM: 7803/1: Fix deadlock scenario with smp_send_stop()")
was trying to fix?

> > > Signed-off-by: Johan Hovold <johan@...nel.org>
> > > ---
> > >  arch/arm/kernel/process.c | 2 --
> > >  1 file changed, 2 deletions(-)
> > > 
> > > diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> > > index a35f6ebbd2c2..5663ab57cf07 100644
> > > --- a/arch/arm/kernel/process.c
> > > +++ b/arch/arm/kernel/process.c
> > > @@ -195,7 +195,6 @@ void machine_halt(void)
> > >  	local_irq_disable();
> > >  	smp_send_stop();
> > >  
> > > -	local_irq_disable();
> > >  	while (1);
> > >  }
> > >  
> > > @@ -237,7 +236,6 @@ void machine_restart(char *cmd)
> > >  
> > >  	/* Whoops - the platform was unable to reboot. Tell the user! */
> > >  	printk("Reboot failed -- System halted\n");
> > > -	local_irq_disable();
> > 
> > ... but wouldn't this reintroduce the the buck which that commit fixed ?
> 
> s/buck/bug :-) my fingers have a mind of their own, aparently.

:)

No, the interrupts would still be disabled.

Thanks,
Johan
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