From: David Miller <davem@davemloft.net>
To: g.nault@alphalink.fr
Cc: jchapman@katalix.com, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org
Subject: Re: [PATCH] l2tp: Restore socket refcount when sendmsg succeeds
Date: Tue, 12 Mar 2013 10:21:21 -0400 (EDT) [thread overview]
Message-ID: <20130312.102121.1471200685376534204.davem@davemloft.net> (raw)
In-Reply-To: <20130312103650.GA4512@alphalink.fr>
From: Guillaume Nault <g.nault@alphalink.fr>
Date: Tue, 12 Mar 2013 11:36:50 +0100
> On Fri, Mar 01, 2013 at 02:12:52PM -0500, David Miller wrote:
>> Looking at how this code works, it is such a terrible design. This
>> whole reference counting issue exists purely because
>> pppol2tp_sock_to_session() grabs the 'sk' reference.
>>
>> In all but one case, it need not do this.
>>
>> The socket system calls have an implicit reference to 'sk' via
>> socket->sk. If you can get into the system call and socket->sk
>> is non-NULL then 'sk' is NOT going anywhere.
>>
>> And all of these system call handlers have this pattern:
>>
>> session = pppol2tp_sock_to_session(sk);
>> ...
>> sock_put(sk);
>>
>> The only case where the reference count is really needed is that
>> sequence in pppol2tp_release().
>>
>> Long term the right thing to do here is stop having this session
>> grabber function take the 'sk' reference. Then in pppol2tp_release
>> we'll grab a reference explicitly. At all the other call sites we
>> then blast aweay all of the sock_put(sk) paths.
>>
> Could this also apply to l2tp_sock_to_tunnel() (in l2tp_core.h)? As per
> my understanding, none of its callers needs to take a socket reference.
> So sock_hold() could be removed in both pppol2tp_sock_to_session() and
> l2tp_sock_to_tunnel() functions. The corresponding sock_put() calls
> would then be removed from all calling functions but pppol2tp_release().
> If this is correct, I'll send a patch for net-next.
Yes, it could be simplified in this way too. Just make sure that this
interface is only used in system call / user context, where we know
the underlying socket cannot go away on us.
prev parent reply other threads:[~2013-03-12 14:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-01 15:02 [PATCH] l2tp: Restore socket refcount when sendmsg succeeds Guillaume Nault
2013-03-01 19:12 ` David Miller
2013-03-12 10:36 ` Guillaume Nault
2013-03-12 14:21 ` David Miller [this message]
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