> On Oct 14, 2024, at 17:04, chenridong <chenridong@xxxxxxxxxx> wrote:
>
>
>
> On 2024/10/14 16:43, Muchun Song wrote:
>>> On Oct 14, 2024, at 16:13, Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote:
>>>
>>>
>>>
>>> On 10/14/24 08:53, Chen Ridong wrote:
>>>> From: Chen Ridong <chenridong@xxxxxxxxxx>
>>>>
>>>> A memleak was found as bellow:
>>>>
>>>> unreferenced object 0xffff8881010d2a80 (size 32):
>>>> comm "mkdir", pid 1559, jiffies 4294932666
>>>> hex dump (first 32 bytes):
>>>> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>>>> 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 @...............
>>>> backtrace (crc 2e7ef6fa):
>>>> [<ffffffff81372754>] __kmalloc_node_noprof+0x394/0x470
>>>> [<ffffffff813024ab>] alloc_shrinker_info+0x7b/0x1a0
>>>> [<ffffffff813b526a>] mem_cgroup_css_online+0x11a/0x3b0
>>>> [<ffffffff81198dd9>] online_css+0x29/0xa0
>>>> [<ffffffff811a243d>] cgroup_apply_control_enable+0x20d/0x360
>>>> [<ffffffff811a5728>] cgroup_mkdir+0x168/0x5f0
>>>> [<ffffffff8148543e>] kernfs_iop_mkdir+0x5e/0x90
>>>> [<ffffffff813dbb24>] vfs_mkdir+0x144/0x220
>>>> [<ffffffff813e1c97>] do_mkdirat+0x87/0x130
>>>> [<ffffffff813e1de9>] __x64_sys_mkdir+0x49/0x70
>>>> [<ffffffff81f8c928>] do_syscall_64+0x68/0x140
>>>> [<ffffffff8200012f>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>>>
>>>> In the alloc_shrinker_info function, when shrinker_unit_alloc return
>>>> err, the info won't be freed. Just fix it.
>>>>
>>>> Fixes: 307bececcd12 ("mm: shrinker: add a secondary array for shrinker_info::{map, nr_deferred}")
>>>> Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
>>>> ---
>>>> mm/shrinker.c | 1 +
>>>> 1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/mm/shrinker.c b/mm/shrinker.c
>>>> index dc5d2a6fcfc4..92270413190d 100644
>>>> --- a/mm/shrinker.c
>>>> +++ b/mm/shrinker.c
>>>> @@ -97,6 +97,7 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
>>>>
>>>> err:
>>>> mutex_unlock(&shrinker_mutex);
>>>> + kvfree(info);
>>>> free_shrinker_info(memcg);
>>>> return -ENOMEM;
>>>> }
>>>
>>> There are two scenarios when "goto err:" gets called
>>>
>>> - When shrinker_info allocations fails, no kvfree() is required
>>> - but after this change kvfree() would be called even
>>> when the allocation had failed originally, which does
>>> not sound right
>> Yes. In this case, @info is NULL and kvfree could handle NULL.
>> It seems strange but the final behaviour correct.
>>>
>>> - shrinker_unit_alloc() fails, kvfree() is actually required
>>>
>>> I guess kvfree() should be called just after shrinker_unit_alloc()
>>> fails but before calling into "goto err".
>> We could do it like this, which avoids ambiguity (if someone ignores
>> that kvfree could handle NULL). Something like:
>> --- a/mm/shrinker.c
>> +++ b/mm/shrinker.c
>> @@ -88,13 +88,14 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
>> goto err;
>> info->map_nr_max = shrinker_nr_max;
>> if (shrinker_unit_alloc(info, NULL, nid))
>> - goto err;
>> + goto free;
>> rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
>> }
>> mutex_unlock(&shrinker_mutex);
>> return ret;
>> -
>> +free:
>> + kvfree(info);
>> err:
>> mutex_unlock(&shrinker_mutex);
>> free_shrinker_info(memcg);
>> Thanks.
>>>
>>> But curious, should not both kvzalloc_node()/kvfree() be avoided
>>> while inside mutex lock to avoid possible lockdep issues ?
> How about:
>
> diff --git a/mm/shrinker.c b/mm/shrinker.c
> index dc5d2a6fcfc4..7baee7f00497 100644
> --- a/mm/shrinker.c
> +++ b/mm/shrinker.c
> @@ -87,9 +87,9 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
> if (!info)
> goto err;
> info->map_nr_max = shrinker_nr_max;
> + rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
> if (shrinker_unit_alloc(info, NULL, nid))
> goto err;
> - rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
> }
> mutex_unlock(&shrinker_mutex);
No. We should make sure the @info is fully initialized before others
could see it. That's why rcu_assign_pointer is used here.
>
> I think this is concise.
>
> Best regards,
> Ridong
