netdev - Re: [PATCH] SCTP: fix race between sctp_bind_addr_free() and sctp_bind_addr

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Message-ID: <BANLkTimoOVytWWTS7Uph_J1401Yxrqr5ug@mail.gmail.com>
Date:	Wed, 18 May 2011 14:06:33 +0200
From:	Jacek Luczak <difrost.kernel@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, Vlad Yasevich <vladislav.yasevich@...com>
Subject: Re: [PATCH] SCTP: fix race between sctp_bind_addr_free() and sctp_bind_addr_conflict()

2011/5/18 Eric Dumazet <eric.dumazet@...il.com>:
> Le mercredi 18 mai 2011 à 10:06 +0200, Jacek Luczak a écrit :
>> 2011/5/18 Eric Dumazet <eric.dumazet@...il.com>:
>
>> > If you're removing items from this list, you must be a writer here, with
>> > exclusive access. So rcu_read_lock()/rcu_read_unlock() is not necessary.
>>
>> I could agree to some extend ... but strict RCU section IMO is needed here.
>> I can check this if the issue exists.
>>
>
> I can tell you for sure rcu_read_lock() is not needed here. Its only
> showing confusion from code's author.
>
> Please read Documentation/RCU/listRCU.txt for concise explanations,
> line 117.
>
>
>> > Therefore, I guess following code is better :
>> >
>> > list_for_each_entry(addr, &bp->address_list, list) {
>> >        list_del_rcu(&addr->list);
>> >        call_rcu(&addr->rcu, sctp_local_addr_free);
>> >        SCTP_DBG_OBJCNT_DEC(addr);
>> > }
>> >
>> > Then, why dont you fix sctp_bind_addr_clean() instead ?
>> >
>> > if 'struct sctp_sockaddr_entry' is recu protected, then all frees should
>> > be protected as well.
>>
>> The _clean() as claimed by Vlad is called many times from various places
>> in code and this could give a overhead. I guess Vlad would need to comment.
>
> I guess a full review of this code is needed. You'll have to prove
> sctp_bind_addr_clean() is always called after one RCU grace period if
> you want to leave it as is.

Eric this is actually good point which I think did not found at first
glance. As the original
issue occurs between _clean() and _conflict() then if the former is
used here and
there we can hit the grace period not only in that case. By that then
_clean() should
be ,,fixed''. Right?

-Jacek
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