linux-kernel - Re: [PATCH v2] memcg: skip cgroup_file

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Message-Id: <20250922164328.0d766c95f9c15330e99514bd@linux-foundation.org>
Date: Mon, 22 Sep 2025 16:43:28 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, Michal
 Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>,
 Muchun Song <muchun.song@...ux.dev>, Alexei Starovoitov <ast@...nel.org>,
 Peilin Ye <yepeilin@...gle.com>, Kumar Kartikeya Dwivedi
 <memxor@...il.com>, bpf@...r.kernel.org, linux-mm@...ck.org,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, Meta kernel team
 <kernel-team@...a.com>, Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v2] memcg: skip cgroup_file_notify if spinning is not
 allowed

On Mon, 22 Sep 2025 16:22:57 -0700 Shakeel Butt <shakeel.butt@...ux.dev> wrote:

> > 
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -2307,12 +2307,13 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
> > >  	bool drained = false;
> > >  	bool raised_max_event = false;
> > >  	unsigned long pflags;
> > > +	bool allow_spinning = gfpflags_allow_spinning(gfp_mask);
> > >  
> > 
> > Does this affect only the problematic call chain which you have
> > identified, or might other callers be undesirably affected?
> 
> It will only affect the call chain which can not spin due to possibly
> NMI context and at the moment only bpf programs can cause that.

"possibly" NMI context?  Is it possible that a bpf caller which could
have taken locks will now skip the notifications?  Or do the gfp_flags
get propagated all the way through?