On 2021/05/13 1:31, Yang Shi wrote:
> On Wed, May 12, 2021 at 5:36 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>>
>> +Tejun Heo
>>
>> On Wed, May 12, 2021 at 3:48 AM NOMURA JUNICHI(野村 淳一)
>> <junichi.nomura@xxxxxxx> wrote:
>>> With the commit 476b30a0949a, if a memcg-aware shrinker is registered before
>>> cgroup_init(), shrinker->nr_deferred is NULL. However xchg_nr_deferred()
>>> tries to use it as memcg is turned off via "cgroup_disable=memory".
>>>
>>> Any thoughts?
>
> Thanks for the report.
>
>>
>> Is there a way to find the call chain of "memcg-aware shrinker is
>> registered before cgroup_init()"?
>
> Other than adding some printk in prealloc_memcg_shrinker() then
> checking out the output of dmesg I didn't think of a better way. Not
> sure if we have something like early trace.
This is the first registration of memcg-aware shrinker:
[ 1.933693] Call Trace:
[ 1.934694] sget_fc+0x20d/0x2f0
[ 1.935693] ? compare_single+0x10/0x10
[ 1.936693] ? shmem_create+0x30/0x30
[ 1.937693] vfs_get_super+0x3e/0x100
[ 1.938693] get_tree_nodev+0x16/0x20
[ 1.939693] shmem_get_tree+0x15/0x20
[ 1.940693] vfs_get_tree+0x2a/0xc0
[ 1.941693] fc_mount+0x12/0x40
[ 1.942693] vfs_kern_mount.part.43+0x61/0xa0
[ 1.943693] kern_mount+0x24/0x40
[ 1.944693] shmem_init+0x5c/0xc8
[ 1.945693] mnt_init+0x12f/0x24a
[ 1.946693] ? __percpu_counter_init+0x8f/0xb0
[ 1.947693] vfs_caches_init+0xce/0xda
[ 1.948693] start_kernel+0x479/0x4e3
[ 1.949693] x86_64_start_reservations+0x24/0x26
[ 1.950693] x86_64_start_kernel+0x8a/0x8d
[ 1.951693] secondary_startup_64_no_verify+0xc2/0xcb
That is done after command line parsing but before cgroup_init.
>> Irrespective I think we can revert a3e72739b7a7e ("cgroup: fix too
>> early usage of static_branch_disable()") as 6041186a3258 ("init:
>> initialize jump labels before command line option parsing") has moved
>> the initialization of jump labels before command line parsing.
>
> Seems make sense to me. If some memcg aware shrinker is registered
> before cgroup_init(), the mem_cgroup_disabled() check in
> prealloc_memcg_shrinker() would return false negative. And I don't
> think any shrinker could be registered before parsing boot
> commandline.
Thank you. Shakeel 's patch works for me:
[PATCH] cgroup: disable controllers at parse time
https://lore.kernel.org/linux-mm/20210512201946.2949351-1-shakeelb@xxxxxxxxxx/
--
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.
