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

[Roman Gushchin <roman.gushchin@linux.dev>]

Shakeel Butt <shakeel.butt@linux.dev> writes:

> 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.

Hmm, what about OOM events? Losing something like MEMCG_LOW doesn't look
like a bit deal, but OOM events can be way more important.

Should we instead preserve the event (e.g. as a pending_event_mask) and
raise it on the next occasion / from a different context?

Thanks