Re: [PATCH -next] arm64/mm: fix a bogus GFP flag in pgd_alloc()

Qian Cai
2019-06-11T12:46:45Z

> On Jun 11, 2019, at 8:41 AM, Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Tue, Jun 11, 2019 at 11:03:49AM +0100, Mark Rutland wrote:
>> On Mon, Jun 10, 2019 at 01:26:15PM -0400, Qian Cai wrote:
>>> On Mon, 2019-06-10 at 12:43 +0100, Will Deacon wrote:
>>>> On Tue, Jun 04, 2019 at 03:23:38PM +0100, Mark Rutland wrote:
>>>>> On Tue, Jun 04, 2019 at 10:00:36AM -0400, Qian Cai wrote:
>>>>>> The commit "arm64: switch to generic version of pte allocation"
>>>>>> introduced endless failures during boot like,
>>>>>>
>>>>>> kobject_add_internal failed for pgd_cache(285:chronyd.service) (error:
>>>>>> -2 parent: cgroup)
>>>>>>
>>>>>> It turns out __GFP_ACCOUNT is passed to kernel page table allocations
>>>>>> and then later memcg finds out those don't belong to any cgroup.
>>>>>
>>>>> Mike, I understood from [1] that this wasn't expected to be a problem,
>>>>> as the accounting should bypass kernel threads.
>>>>>
>>>>> Was that assumption wrong, or is something different happening here?
>>>>>
>>>>>>
>>>>>> backtrace:
>>>>>> kobject_add_internal
>>>>>> kobject_init_and_add
>>>>>> sysfs_slab_add+0x1a8
>>>>>> __kmem_cache_create
>>>>>> create_cache
>>>>>> memcg_create_kmem_cache
>>>>>> memcg_kmem_cache_create_func
>>>>>> process_one_work
>>>>>> worker_thread
>>>>>> kthread
>>>>>>
>>>>>> Signed-off-by: Qian Cai <cai@lca.pw>
>>>>>> ---
>>>>>> arch/arm64/mm/pgd.c | 2 +-
>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
>>>>>> index 769516cb6677..53c48f5c8765 100644
>>>>>> --- a/arch/arm64/mm/pgd.c
>>>>>> +++ b/arch/arm64/mm/pgd.c
>>>>>> @@ -38,7 +38,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
>>>>>> if (PGD_SIZE == PAGE_SIZE)
>>>>>> return (pgd_t *)__get_free_page(gfp);
>>>>>> else
>>>>>> - return kmem_cache_alloc(pgd_cache, gfp);
>>>>>> + return kmem_cache_alloc(pgd_cache, GFP_PGTABLE_KERNEL);
>>>>>
>>>>> This is used to allocate PGDs for both user and kernel pagetables (e.g.
>>>>> for the efi runtime services), so while this may fix the regression, I'm
>>>>> not sure it's the right fix.
>>>>>
>>>>> Do we need a separate pgd_alloc_kernel()?
>>>>
>>>> So can I take the above for -rc5, or is somebody else working on a different
>>>> fix to implement pgd_alloc_kernel()?
>>>
>>> The offensive commit "arm64: switch to generic version of pte allocation" is not
>>> yet in the mainline, but only in the Andrew's tree and linux-next, and I doubt
>>> Andrew will push this out any time sooner given it is broken.
>>
>> I'd assumed that Mike would respin these patches to implement and use
>> pgd_alloc_kernel() (or take gfp flags) and the updated patches would
>> replace these in akpm's tree.
>>
>> Mike, could you confirm what your plan is? I'm happy to review/test
>> updated patches for arm64.
>
> Sorry for the delay, I'm mostly offline these days.
>
> I wanted to understand first what is the reason for the failure. I've tried
> to reproduce it with qemu, but I failed to find a bootable configuration
> that will have PGD_SIZE != PAGE_SIZE :(
>
> Qian Cai, can you share what is your environment and the kernel config?

https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config

# lscpu
Architecture: aarch64
Byte Order: Little Endian
CPU(s): 256
On-line CPU(s) list: 0-255
Thread(s) per core: 4
Core(s) per socket: 32
Socket(s): 2
NUMA node(s): 2
Vendor ID: Cavium
Model: 1
Model name: ThunderX2 99xx
Stepping: 0x1
BogoMIPS: 400.00
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 32768K
NUMA node0 CPU(s): 0-127
NUMA node1 CPU(s): 128-255
Flags: fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics cpuid asimdrdm

# dmidecode
Handle 0x0001, DMI type 1, 27 bytes
System Information
Manufacturer: HPE
Product Name: Apollo 70
Version: X1
Wake-up Type: Power Switch
Family: CN99XX