netdev - Re: [PATCH v2 bpf-next 13/13] bpf: Convert bpf_cpumask to bpf_mem_cache_free

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Date: Mon, 26 Jun 2023 13:01:47 -0500
From: David Vernet <void@...ifault.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Hou Tao <houtao@...weicloud.com>,
	"Paul E. McKenney" <paulmck@...nel.org>, Tejun Heo <tj@...nel.org>,
	rcu@...r.kernel.org, Network Development <netdev@...r.kernel.org>,
	bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 13/13] bpf: Convert bpf_cpumask to
 bpf_mem_cache_free_rcu.

On Mon, Jun 26, 2023 at 10:59:40AM -0700, Alexei Starovoitov wrote:
> On Mon, Jun 26, 2023 at 10:55 AM David Vernet <void@...ifault.com> wrote:
> >
> > > > > +
> > > > > +     migrate_disable();
> > > > > +     bpf_mem_cache_free_rcu(&bpf_cpumask_ma, cpumask);
> > > > > +     migrate_enable();
> > > >
> > > > The fact that callers have to disable migration like this in order to
> > > > safely free the memory feels a bit leaky. Is there any reason we can't
> > > > move this into bpf_mem_{cache_}free_rcu()?
> > >
> > > migrate_disable/enable() are actually not necessary here.
> > > We can call bpf_mem_cache_free_rcu() directly from any kfunc.
> >
> > Could you please clarify why? Can't we migrate if the kfunc is called
> > from a sleepable struct_ops callback?
> 
> migration is disabled for all bpf progs including sleepable.

Fair enough :-) Then yep, let's remove these. Feel free to do so when
you send v2, and keep my Ack. Otherwise I'm happy to send a follow-on
patch after this series is merged.