From: Stanislav Fomichev <sdf@fomichev.me>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Stanislav Fomichev <sdf@google.com>,
Network Development <netdev@vger.kernel.org>,
bpf <bpf@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH bpf 0/4] bpf: remove __rcu annotations from bpf_prog_array
Date: Tue, 14 May 2019 19:11:44 -0700 [thread overview]
Message-ID: <20190515021144.GD10244@mini-arch> (raw)
In-Reply-To: <CAADnVQLAJ77XS8vfdnszHsw_KcmzrMDvPH0UxVXORN-wjc=rWQ@mail.gmail.com>
On 05/14, Alexei Starovoitov wrote:
> On Tue, May 14, 2019 at 10:53 AM Stanislav Fomichev <sdf@fomichev.me> wrote:
> >
> > Existing __rcu annotations don't add anything to the safety.
>
> what do you mean?
> BPF_PROG_RUN_ARRAY derefs these pointers under rcu.
And I'm not removing them from the struct definitions, I'm removing __rcu
from the helpers' arguments only. Because those helpers are always called
with the mutex and don't need it. To reiterate: rcu_dereference_protected
is enough to get a pointer (from __rcu annotated) for the duration
of the mutex, helpers can operate on the non-annotated (dereferenced) prog
array.
Read section still does the following (BPF_PROG_RUN_ARRAY):
rcu_read_lock();
p = rcu_dereference(__rcu'd progs);
while (p) {}
rcu_read_unlock();
And write sections do:
mutex_lock(&mtx);
p = rcu_dereference_protected(__rcu'd progs, lockdep_is_held(&mtx);
// ^^^ does rcu_dereference in the mutex protected section
bpf_prog_array_length(p);
bpf_prog_array_copy_to_user(p, ...);
bpf_prog_array_delete_safe(p);
bpf_prog_array_copy_info(p);
bpf_prog_array_copy(p, ...);
bpf_prog_array_free(p);
// ^^^ all these helpers are consistent already with or
// without __rcu annotation because we hold a mutex and
// guarantee no concurrent updates, so __rcu annotations
// for their input arguments is not needed.
mutex_unlock(&mtx);
next prev parent reply other threads:[~2019-05-15 2:14 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-08 17:18 [PATCH bpf 0/4] bpf: remove __rcu annotations from bpf_prog_array Stanislav Fomichev
2019-05-08 17:18 ` [PATCH bpf 1/4] " Stanislav Fomichev
2019-05-08 17:18 ` [PATCH bpf 2/4] bpf: media: properly use bpf_prog_array api Stanislav Fomichev
2019-05-08 17:18 ` [PATCH bpf 3/4] bpf: cgroup: " Stanislav Fomichev
2019-05-08 17:18 ` [PATCH bpf 4/4] bpf: tracing: " Stanislav Fomichev
2019-05-08 17:56 ` [PATCH bpf 0/4] bpf: remove __rcu annotations from bpf_prog_array Alexei Starovoitov
2019-05-08 18:12 ` Stanislav Fomichev
2019-05-13 18:57 ` Stanislav Fomichev
2019-05-14 16:55 ` Alexei Starovoitov
2019-05-14 17:30 ` Stanislav Fomichev
2019-05-14 17:45 ` Alexei Starovoitov
2019-05-14 17:53 ` Stanislav Fomichev
2019-05-15 1:25 ` Alexei Starovoitov
2019-05-15 2:11 ` Stanislav Fomichev [this message]
2019-05-15 2:27 ` Alexei Starovoitov
2019-05-15 2:44 ` Eric Dumazet
2019-05-15 2:56 ` Stanislav Fomichev
2019-05-15 3:16 ` Alexei Starovoitov
2019-05-15 3:38 ` Stanislav Fomichev
2019-05-15 3:42 ` Alexei Starovoitov
2019-05-15 3:49 ` Stanislav Fomichev
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