netdev - Re: [RFC PATCH bpf-next 2/6] bpf: add bpf_get

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <49c15114-c518-b591-470a-b4073a675588@fb.com>
Date:   Sun, 8 Apr 2018 22:02:38 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Yonghong Song <yhs@...com>, <daniel@...earbox.net>,
        <netdev@...r.kernel.org>
CC:     <kernel-team@...com>
Subject: Re: [RFC PATCH bpf-next 2/6] bpf: add bpf_get_stack helper

On 4/8/18 9:53 PM, Yonghong Song wrote:
>>> @@ -1004,7 +1007,8 @@ static void __bpf_prog_put(struct bpf_prog
>>> *prog, bool do_idr_lock)
>>>              bpf_prog_kallsyms_del(prog->aux->func[i]);
>>>          bpf_prog_kallsyms_del(prog);
>>>
>>> -        call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu);
>>> +        synchronize_rcu();
>>> +        __bpf_prog_put_rcu(&prog->aux->rcu);
>>
>> there should have been lockdep splat.
>> We cannot call synchronize_rcu here, since we cannot sleep
>> in some cases.
>
> Let me double check this. The following is the reason
> why I am using synchronize_rcu().
>
> With call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu) and
> _bpf_prog_put_rcu calls put_callchain_buffers() which
> calls mutex_lock(), the runtime with CONFIG_DEBUG_ATOMIC_SLEEP=y
> will complains since potential sleep inside the call_rcu is not
> allowed.

I see. Indeed. We cannot call put_callchain_buffers() from rcu callback,
but doing synchronize_rcu() here is also not possible.
How about moving put_callchain into bpf_prog_free_deferred() ?