linux-kernel - Re: mmotm 2010-04-28

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Message-ID: <4BE82E39.6080603@trash.net>
Date:	Mon, 10 May 2010 18:03:05 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, Valdis.Kletnieks@...edu,
	akpm@...ux-foundation.org, peterz@...radead.org,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: mmotm 2010-04-28 - RCU whinges

Eric Dumazet wrote:
> Le lundi 10 mai 2010 à 17:40 +0200, Patrick McHardy a écrit :
>> David Miller wrote:
>>> From: Eric Dumazet <eric.dumazet@...il.com>
>>> Date: Mon, 03 May 2010 07:43:56 +0200
>>>
>>>> Le lundi 03 mai 2010 à 07:41 +0200, Eric Dumazet a écrit :
>>>>
>>>>> Oops scratch that, I'll resend a correct version.
>>>>>
>>>>>
>>>> Sorry, patch _is_ fine, I had one brain collapse when re-reading it, I
>>>> thought a different mutex was in use in one of the functions.
>>> Ok, Patrick please review, thanks.
>> Actually we don't need the rcu_dereference() calls at all since
>> registration and unregistration are protected by the mutexes.
>>
>> I queued this patch in nf-next, the only reason why I haven't
>> submitted it yet is that I was unable to get git to cleanly export
>> only the proper set of patches meant for -next due to a few merges,
>> it insists on including 5 patches already merged upstream. If you
>> don't mind ignoring the first 5 patches in the series, I'll send a
>> pull request tonight.
>>
> 
> This will clash with upcoming RCU patches, where rcu protected pointer
> cannot be directly accessed without lockdep splats.
> 
> We will need one day or another a rcu_...(nf_conntrack_event_cb)

Thanks for the information, I didn't realize that when looking at
those patches. So I guess the correct fix once those patches are
merged would be to use rcu_assign_protected() and rcu_access_pointer().
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