Re: kmemleak: Unable to handle kernel paging request

[Denis Kirjanov <kda@linux-powerpc.org>]

On 6/13/14, Catalin Marinas <catalin.marinas@arm.com> wrote:
> On Fri, Jun 13, 2014 at 08:12:08AM +0100, Denis Kirjanov wrote:
>> On 6/12/14, Catalin Marinas <catalin.marinas@arm.com> wrote:
>> > On Thu, Jun 12, 2014 at 01:00:57PM +0100, Denis Kirjanov wrote:
>> >> On 6/12/14, Denis Kirjanov <kda@linux-powerpc.org> wrote:
>> >> > On 6/12/14, Catalin Marinas <catalin.marinas@arm.com> wrote:
>> >> >> On 11 Jun 2014, at 21:04, Denis Kirjanov <kda@linux-powerpc.org>
>> >> >> wrote:
>> >> >>> On 6/11/14, Catalin Marinas <catalin.marinas@arm.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
>
> OK, so that's the DART table allocated via alloc_dart_table(). Is
> dart_tablebase removed from the kernel linear mapping after allocation?
> If that's the case, we need to tell kmemleak to ignore this block (see
> patch below, untested). But I still can't explain how commit
> d4c54919ed863020 causes this issue.
>
> (also cc'ing the powerpc list and maintainers)

Ok, your path fixes the oops.

Ben, can you shed some light on this issue?

Thanks!
> ---------------8<--------------------------
>
> From 09a7f1c97166c7bdca7ca4e8a4ff2774f3706ea3 Mon Sep 17 00:00:00 2001
> From: Catalin Marinas <catalin.marinas@arm.com>
> Date: Fri, 13 Jun 2014 09:44:21 +0100
> Subject: [PATCH] powerpc/kmemleak: Do not scan the DART table
>
> The DART table allocation is registered to kmemleak via the
> memblock_alloc_base() call. However, the DART table is later unmapped
> and dart_tablebase VA no longer accessible. This patch tells kmemleak
> not to scan this block and avoid an unhandled paging request.
>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> ---
>  arch/powerpc/sysdev/dart_iommu.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/powerpc/sysdev/dart_iommu.c
> b/arch/powerpc/sysdev/dart_iommu.c
> index 62c47bb76517..9e5353ff6d1b 100644
> --- a/arch/powerpc/sysdev/dart_iommu.c
> +++ b/arch/powerpc/sysdev/dart_iommu.c
> @@ -476,6 +476,11 @@ void __init alloc_dart_table(void)
>  	 */
>  	dart_tablebase = (unsigned long)
>  		__va(memblock_alloc_base(1UL<<24, 1UL<<24, 0x80000000L));
> +	/*
> +	 * The DART space is later unmapped from the kernel linear mapping and
> +	 * accessing dart_tablebase during kmemleak scanning will fault.
> +	 */
> +	kmemleak_no_scan((void *)dart_tablebase);
>
>  	printk(KERN_INFO "DART table allocated at: %lx\n", dart_tablebase);
>  }
>

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