netdev - Re: [PATCH net] sctp: check duplicate node before inserting a new transport

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Message-ID: <CADvbK_dvJoEvmx1PvemxUS1090J1o=Gx3COPK7rdHT4Z1z27UQ@mail.gmail.com>
Date:   Sat, 18 Feb 2017 23:47:38 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Vlad Yasevich <vyasevich@...il.com>
Subject: Re: [PATCH net] sctp: check duplicate node before inserting a new transport

On Sat, Feb 18, 2017 at 4:19 AM, David Miller <davem@...emloft.net> wrote:
> From: Xin Long <lucien.xin@...il.com>
> Date: Fri, 17 Feb 2017 16:35:24 +0800
>
>
>> +     list = rhltable_lookup(&sctp_transport_hashtable, &arg,
>> +                            sctp_hash_params);
>> +
>> +     rhl_for_each_entry_rcu(transport, tmp, list, node)
>> +             if (transport->asoc->ep == t->asoc->ep) {
>> +                     err = -EEXIST;
>> +                     goto out;
>> +             }
>> +
>>       err = rhltable_insert_key(&sctp_transport_hashtable, &arg,
>>                                 &t->node, sctp_hash_params);
>> +
>> +out:
>
> Well, what if another thread of control inserts a matching transport
> after you've checked the list but before rhltable_insert_key() does
> it's work?
>
> What write side lock is being held to protect the table from
> modifications here?
sock lock.
...
sctp_assoc_add_peer()
  sctp_hash_transport()
     rhltable_insert_key()

all the places where it call  sctp_assoc_add_peer() are proctected by
lock_sock(). it's a big lock, no need to worry about race issues here.