linux-kernel - Re: 3.10.9: kmemleak disables all CPUs except CPU0

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Date:	Mon, 2 Sep 2013 17:09:08 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Martin MOKREJŠ <mmokrejs@...il.com>
Cc:	Max Filippov <jcmvbkbc@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 3.10.9: kmemleak disables all CPUs except CPU0

On Mon, Sep 02, 2013 at 04:51:17PM +0100, Martin MOKREJŠ wrote:
> Catalin Marinas wrote:
> > On Mon, Sep 02, 2013 at 04:44:52PM +0100, Max Filippov wrote:
> >> On Mon, Sep 2, 2013 at 7:31 PM, Catalin Marinas <catalin.marinas@....com> wrote:
> >>> On 31 August 2013 14:35, Martin MOKREJŠ <mmokrejs@...il.com> wrote:
> >>>>   never realized that my CPUs are gone if I compile into kernel kmemleak.
> >>>> Is that really the aim?
> >>>>
> >>>> CONFIG_HAVE_DEBUG_KMEMLEAK=y
> >>>> CONFIG_DEBUG_KMEMLEAK=y
> >>>> CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE=400
> >>>> # CONFIG_DEBUG_KMEMLEAK_TEST is not set
> >>>> # CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF is not set
> >>>>
> >>>> 1.  Why isn't there /sys/devices/system/cpu/cpu0/online file?
> >>>> Does not matter if it contains 0 or 1. It just should exist.
> >>>
> >>> I can't really see how kmemleak would do this, maybe other config
> >>> options that get set/cleared in the process of selecting kmemleak. Can
> >>
> >> Seems to be kmemcheck: from arch/x86/mm/kmemcheck/kmemcheck.c:
> >>
> >> int __init kmemcheck_init(void)
> >> {
> >> #ifdef CONFIG_SMP
> >>         /*
> >>          * Limit SMP to use a single CPU. We rely on the fact that this code
> >>          * runs before SMP is set up.
> >>          */
> >>         if (setup_max_cpus > 1) {
> >>                 printk(KERN_INFO
> >>                         "kmemcheck: Limiting number of CPUs to 1.\n");
> >>                 setup_max_cpus = 1;
> >>         }
> >> #endif
> > 
> > Ah, ok, not my problem then ;)
> 
> Fine, so would somebody please update the help text accessible in "menuconfig"
> for this entry? It should be clear that it has a huge performance impact if enabled.
> And, by compiling in it is enabled by default.

Otherwise, of no-one volunteers, please feel free to send a patch ;)

-- 
Catalin
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