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

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Date:	Fri, 13 Jun 2014 11:12:08 +0400
From:	Denis Kirjanov <kda@...ux-powerpc.org>
To:	Catalin Marinas <catalin.marinas@....com>
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 6/12/14, Catalin Marinas <catalin.marinas@....com> wrote:
> 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.

The address is always the same.

[  179.466239] kmemleak: Object 0xc00000007f000000 (size 16777216):
[  179.466503] kmemleak:   comm "swapper/0", pid 0, jiffies 4294892300
[  179.466508] kmemleak:   min_count = 0
[  179.466512] kmemleak:   count = 0
[  179.466517] kmemleak:   flags = 0x1
[  179.466522] kmemleak:   checksum = 0
[  179.466526] kmemleak:   backtrace:
[  179.466531]      [<c000000000afc3dc>] .memblock_alloc_range_nid+0x68/0x88
[  179.466544]      [<c000000000afc444>] .memblock_alloc_base+0x20/0x58
[  179.466553]      [<c000000000ae96cc>] .alloc_dart_table+0x5c/0xb0
[  179.466561]      [<c000000000aea300>] .pmac_probe+0x38/0xa0
[  179.466569]      [<000000000002166c>] 0x2166c
[  179.466579]      [<0000000000ae0e68>] 0xae0e68
[  179.466587]      [<0000000000009bc4>] 0x9bc4


> --
> Catalin
>
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