netdev - Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around __sk_dst

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Message-ID: <56FDF541.6070106@stressinduktion.org>
Date:	Fri, 1 Apr 2016 06:12:49 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	sasha.levin@...cle.com, daniel@...earbox.net, mkubecek@...e.cz
Subject: Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around
 __sk_dst_get

On 01.04.2016 06:04, Alexei Starovoitov wrote:
> On Thu, Mar 31, 2016 at 08:03:38PM -0700, Eric Dumazet wrote:
>> On Thu, 2016-03-31 at 18:45 -0700, Alexei Starovoitov wrote:
>>
>>> Eric, what's your take on Hannes's patch 2 ?
>>> Is it more accurate to ask lockdep to check for actual lock
>>> or lockdep can rely on owned flag?
>>> Potentially there could be races between setting the flag and
>>> actual lock... but that code is contained, so unlikely.
>>> Will we find the real issues with this 'stronger' check or
>>> just spend a ton of time adapting to new model like your other
>>> patch for release_sock and whatever may need to come next...
>>
>> More precise lockdep checks are certainly good, I only objected to 4/4
>> trying to work around another bug.
>>
>> But why do we rush for 'net' tree ?
>>
>> This looks net-next material to me.
>>
>> Locking changes are often subtle, lets take the time to do them
>> properly.
>
> completely agree. I think only first patch belongs in net.
> Everything else is net-next material.

Problem with first patch is that it uses lock_sock_fast, thus the 
current sock_owned_by_user check doesn't get rid the lockdep warning. :/

Thus we would need to go with the two first patches. Do you think it is 
acceptable? I actually didn't see a problem and testing showed no 
problems so far.

Bye,
Hannes