linux-kernel - Re: [PATCH -next] arm64/mm: fix a bogus GFP flag in pgd

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Message-Id: <3F6E1B9F-3789-4648-B95C-C4243B57DA02@lca.pw>
Date:   Tue, 11 Jun 2019 08:46:45 -0400
From:   Qian Cai <cai@....pw>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        catalin.marinas@....com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        mhocko@...nel.org, linux-mm@...ck.org, vdavydov.dev@...il.com,
        hannes@...xchg.org, cgroups@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH -next] arm64/mm: fix a bogus GFP flag in pgd_alloc()



> On Jun 11, 2019, at 8:41 AM, Mike Rapoport <rppt@...ux.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@....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