> 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 ?
