linux-kernel - Re: [V3 PATCH] x86: avoid calling arch_trigger_all_cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 11 Nov 2010 09:34:25 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Dongdong Deng <dongdong.deng@...driver.com>, peterz@...radead.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [V3 PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace()
 at the same time on SMP

On Thu, Nov 11, 2010 at 12:17:02PM +0100, Ingo Molnar wrote:
> 
> Hm, another thing i noticed is that there's two of these:

I guess it depends how we want to deprecate the old nmi watchdog.
Dongdong was just patching the old and new code.

There are 3 ways we can go here.

- rip out the 'arch_trigger_all_cpu_backtrace' from the old nmi_watchdog,
  rework the Makefile and have both watchdogs use common code in hw_nmi.c

- patch both places

- rely on the fact that the old watchdog doesn't really work any more and
  only patch the new watchdog

I can put together a patch to do the first one, then have Dongdong put his
patch on top.  Selfishly I wouldn't mind just doing the third option. ;-)

Thoughts?

Cheers,
Don

> 
> >  #ifdef ARCH_HAS_NMI_WATCHDOG
> > +/* "in progress" flag of arch_trigger_all_cpu_backtrace */
> > +static unsigned long backtrace_flag;
> > +
> >  void arch_trigger_all_cpu_backtrace(void)
> >  {
> >  	int i;
> > +	unsigned long flags;
> > +
> > +	/*
> > +	 * Have to disable irq here, as the
> > +	 * arch_trigger_all_cpu_backtrace() could be
> > +	 * triggered by "spin_lock()" with irqs on.
> > +	 */
> > +	local_irq_save(flags);
> 
> > +/* "in progress" flag of arch_trigger_all_cpu_backtrace */
> > +static unsigned long backtrace_flag;
> > +
> >  void arch_trigger_all_cpu_backtrace(void)
> >  {
> >  	int i;
> > +	unsigned long flags;
> > +
> > +	/*
> > +	 * Have to disable irq here, as the
> > +	 * arch_trigger_all_cpu_backtrace() could be
> > +	 * triggered by "spin_lock()" with irqs on.
> > +	 */
> > +	local_irq_save(flags);
> > +
> > +	if (test_and_set_bit(0, &backtrace_flag))
> 
> A fair amount of code is being duplicated in two places - which is not nice. Lets 
> try to create a shared facility instead?
> 
> Thanks,
> 
> 	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/