linux-kernel - Re: kmemleak: Unable to handle kernel paging request

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Date:	Thu, 12 Jun 2014 15:39:16 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Denis Kirjanov <kda@...ux-powerpc.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: kmemleak: Unable to handle kernel paging request

On Thu, Jun 12, 2014 at 01:00:57PM +0100, Denis Kirjanov wrote:
> On 6/12/14, Denis Kirjanov <kda@...ux-powerpc.org> wrote:
> > On 6/12/14, Catalin Marinas <catalin.marinas@....com> wrote:
> >> On 11 Jun 2014, at 21:04, Denis Kirjanov <kda@...ux-powerpc.org> wrote:
> >>> On 6/11/14, Catalin Marinas <catalin.marinas@....com> wrote:
> >>>> On Wed, Jun 11, 2014 at 04:13:07PM +0400, Denis Kirjanov wrote:
> >>>>> I got a trace while running 3.15.0-08556-gdfb9454:
> >>>>>
> >>>>> [  104.534026] Unable to handle kernel paging request for data at
> >>>>> address 0xc00000007f000000
> >>>>
> >>>> Were there any kmemleak messages prior to this, like "kmemleak
> >>>> disabled"? There could be a race when kmemleak is disabled because of
> >>>> some fatal (for kmemleak) error while the scanning is taking place
> >>>> (which needs some more thinking to fix properly).
> >>>
> >>> No. I checked for the similar problem and didn't find anything relevant.
> >>> I'll try to bisect it.
> >>
> >> Does this happen soon after boot? I guess it’s the first scan
> >> (scheduled at around 1min after boot). Something seems to be telling
> >> kmemleak that there is a valid memory block at 0xc00000007f000000.
> >
> > Yeah, it happens after a while with a booted system so that's the
> > first kmemleak scan.
> >
> 
> I've bisected to this commit: d4c54919ed86302094c0ca7d48a8cbd4ee753e92
> "mm: add !pte_present() check on existing hugetlb_entry callbacks".
> Reverting the commit fixes the issue

I can't figure how this causes the problem but I have more questions. Is
0xc00000007f000000 address always the same in all crashes? If yes, you
could comment out start_scan_thread() in kmemleak_late_init() to avoid
the scanning thread starting. Once booted, you can run:

  echo dump=0xc00000007f000000 > /sys/kernel/debug/kmemleak

and check the dmesg for what kmemleak knows about that address, when it
was allocated and whether it should be mapped or not.

-- 
Catalin
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