linux-kernel - Re: net/sctp: recursive locking in sctp_do

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Message-ID: <CAM_iQpVY3QOdvCOsinJ=v2CF1M0c+XV2o80ec=qDyithuqeACw@mail.gmail.com>
Date:   Wed, 15 Mar 2017 11:19:38 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Vladislav Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        David Miller <davem@...emloft.net>, linux-sctp@...r.kernel.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/sctp: recursive locking in sctp_do_peeloff

On Wed, Mar 15, 2017 at 5:52 AM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> On Tue, Mar 14, 2017 at 09:52:15PM -0700, Cong Wang wrote:
>> Instead of checking for the status of the sock, I believe the following
>> one-line fix should do the trick too. Can you give it a try?
>>
>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>> index 0f378ea..4de62d4 100644
>> --- a/net/sctp/socket.c
>> +++ b/net/sctp/socket.c
>> @@ -1494,7 +1494,7 @@ static void sctp_close(struct sock *sk, long timeout)
>>
>>         pr_debug("%s: sk:%p, timeout:%ld\n", __func__, sk, timeout);
>>
>> -       lock_sock(sk);
>> +       lock_sock_nested(sk, SINGLE_DEPTH_NESTING);
>>         sk->sk_shutdown = SHUTDOWN_MASK;
>>         sk->sk_state = SCTP_SS_CLOSING;
>
> I refrained on doing this just because it will change the lock signature
> for the first level too, as sctp_close() can be called directly, and
> might avoid some other lockdep detections.

I knew, but for the first level it is fine to use a different class,
it is merely to make lockdep happy. There is no real deadlock here
since they are two different socks anyway.

>
> Then you probably also need:
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 465a9c8464f9..02506b4406d2 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -1543,7 +1543,7 @@ static void sctp_close(struct sock *sk, long timeout)
>          * held and that should be grabbed before socket lock.
>          */
>         spin_lock_bh(&net->sctp.addr_wq_lock);
> -       bh_lock_sock(sk);
> +       bh_lock_sock_nested(sk);
>
>         /* Hold the sock, since sk_common_release() will put sock_put()
>          * and we have just a little more cleanup.
>
> because sctp_close will re-lock the socket a little later (for backlog
> processing).
>

Ah, of course I missed the re-lock. Dmitry, please add this piece too.

Thanks.