Re: [PATCH bpf-next v2] bpf: move rcu lock management out of BPF_PROG_RUN routines

From: Martin KaFai Lau <kafai@fb.com>
To: Stanislav Fomichev <sdf@google.com>
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, ast@kernel.org,
	daniel@iogearbox.net, andrii@kernel.org
Subject: Re: [PATCH bpf-next v2] bpf: move rcu lock management out of BPF_PROG_RUN routines
Date: Thu, 14 Apr 2022 13:23:45 -0700	[thread overview]
Message-ID: <20220414202345.kireigrz7jftmes4@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20220414161233.170780-1-sdf@google.com>

On Thu, Apr 14, 2022 at 09:12:33AM -0700, Stanislav Fomichev wrote:
> Commit 7d08c2c91171 ("bpf: Refactor BPF_PROG_RUN_ARRAY family of macros
> into functions") switched a bunch of BPF_PROG_RUN macros to inline
> routines. This changed the semantic a bit. Due to arguments expansion
> of macros, it used to be:
> 
> 	rcu_read_lock();
> 	array = rcu_dereference(cgrp->bpf.effective[atype]);
> 	...
> 
> Now, with with inline routines, we have:
> 	array_rcu = rcu_dereference(cgrp->bpf.effective[atype]);
> 	/* array_rcu can be kfree'd here */
> 	rcu_read_lock();
> 	array = rcu_dereference(array_rcu);
> 
> I'm assuming in practice rcu subsystem isn't fast enough to trigger
> this but let's use rcu API properly.
> 
> Also, rename to lower caps to not confuse with macros. Additionally,
> drop and expand BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY.
> 
> See [1] for more context.
> 
>   [1] https://lore.kernel.org/bpf/CAKH8qBs60fOinFdxiiQikK_q0EcVxGvNTQoWvHLEUGbgcj1UYg@mail.gmail.com/T/#u
> 
> v2
> - keep rcu locks inside by passing cgroup_bpf
Acked-by: Martin KaFai Lau <kafai@fb.com>