linux-kernel - Re: [BUG 4.2-rc8] Interrupt occurs while apply

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Message-ID: <20150904074049.GM29283@redhat.com>
Date:	Fri, 4 Sep 2015 08:40:49 +0100
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Borislav Petkov <bp@...en8.de>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is
 patching the handler

On Thu, Sep 03, 2015 at 12:41:47PM +0200, Thomas Gleixner wrote:
> On Thu, 3 Sep 2015, Borislav Petkov wrote:
> > On Wed, Sep 02, 2015 at 11:11:55AM +0200, Thomas Gleixner wrote:
> > >  static void __init_or_module add_nops(void *insns, unsigned int len)
> > >  {
> > > +	unsigned long flags;
> > > +
> > > +	local_irq_save(flags);
> > >  	while (len > 0) {
> > 
> > I guess you want to optimize the len==0 case to not disable interrupts
> > needlessly:
> > 
> > 	if (!len)
> > 		return;
> > 
> > 	local_irq_save(flags);
> > 	while (len > 0)
> > 		...
> 
> Nah. I rather put the local_irq_save into optimize_nops(). All other
> callers of add_nops() are operating on a buffer and use text_poke
> after that. Aside of that optimize_nops() is missing a sync_core().
> 
> Updated patch below.

V2 of the patch managed ~ 5000 iterations overnight without hitting
the problem, so looks like it's a good fix.

Thanks, Rich.

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