Re: [PATCH] memcg: skip cgroup_file_notify if spinning is not allowed

[Peilin Ye <yepeilin@google.com>]

On Fri, Sep 05, 2025 at 01:16:06PM -0700, Shakeel Butt wrote:
> Generally memcg charging is allowed from all the contexts including NMI
> where even spinning on spinlock can cause locking issues. However one
> call chain was missed during the addition of memcg charging from any
> context support. That is try_charge_memcg() -> memcg_memory_event() ->
> cgroup_file_notify().
> 
> The possible function call tree under cgroup_file_notify() can acquire
> many different spin locks in spinning mode. Some of them are
> cgroup_file_kn_lock, kernfs_notify_lock, pool_workqeue's lock. So, let's
> just skip cgroup_file_notify() from memcg charging if the context does
> not allow spinning.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

Tested-by: Peilin Ye <yepeilin@google.com>

The repro described in [1] no longer triggers locking issues after
applying this patch and making __bpf_async_init() use __GFP_HIGH
instead of GFP_ATOMIC:

--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1275,7 +1275,7 @@ static int __bpf_async_init(struct bpf_async_kern *async, struct bpf_map *map, u
        }

        /* allocate hrtimer via map_kmalloc to use memcg accounting */
-       cb = bpf_map_kmalloc_node(map, size, GFP_ATOMIC, map->numa_node);
+       cb = bpf_map_kmalloc_node(map, size, __GFP_HIGH, map->numa_node);
        if (!cb) {
                ret = -ENOMEM;
                goto out;

[1] https://lore.kernel.org/bpf/20250905061919.439648-1-yepeilin@google.com/#t

Thanks,
Peilin Ye