[PATCH] mm: shrinker: avoid memleak in alloc_shrinker_info

[Qi Zheng <zhengqi.arch@bytedance.com>]

On 2024/10/11 22:21, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> 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}")

I think this also needs to be cc'd to the stable mailing list:

Cc: stable@vger.kernel.org

> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> ---
>   mm/shrinker.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)

Other than that, LGTM.

Acked-by: Qi Zheng <zhengqi.arch@bytedance.com>

Thanks!

> 
> diff --git a/mm/shrinker.c b/mm/shrinker.c
> index dc5d2a6fcfc4..e4b795ee6d2e 100644
> --- a/mm/shrinker.c
> +++ b/mm/shrinker.c
> @@ -87,8 +87,10 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
>   		if (!info)
>   			goto err;
>   		info->map_nr_max = shrinker_nr_max;
> -		if (shrinker_unit_alloc(info, NULL, nid))
> +		if (shrinker_unit_alloc(info, NULL, nid)) {
> +			kvfree(info);
>   			goto err;
> +		}
>   		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
>   	}
>   	mutex_unlock(&shrinker_mutex);