netdev - Re: [PATCH v2 net 2/2] net sched actions: decrement module refcount earlier

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Date:   Thu, 20 Apr 2017 06:24:54 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Wolfgang Bumiller <w.bumiller@...xmox.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2 net 2/2] net sched actions: decrement module refcount
 earlier

On 17-04-19 11:03 AM, Wolfgang Bumiller wrote:
>> On April 19, 2017 at 1:32 PM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>>
>>
>> On 17-04-19 04:09 AM, Wolfgang Bumiller wrote:
>>
>> This solves one issue, but I am afraid the issue Cong mentioned is a
>> possibility still.
>> Lets say user did a replace and tried to also replace the cookie
>> in that transaction. The init() succeeds but the cookie allocation
>> fails. To be correct we'll have to undo the replace i.e something
>> like uninit() which will restore back the old values.
>> This is very complex and unnecessary.
>>
>> My suggestion:
>> If we move the cookie allocation before init we can save it and
>> only when init succeeds do we attach it to the action, otherwise
>> we free it on error path.
>
> Shouldn't the old code have freed an old a->act_cookie as well before
> replacing it then? nla_memdup_cookie() starts off by assigning a->act_cookie.
>
> (I've been running this loop for a while now:
> # while : ; do tc actions change action ok index 500 cookie $i; let i++; done
> and memory usage *seems* to be growing faster with the loop running - still
> slow, but visible. (I stopped most but not all background processes in this
> VM))
>
> I don't see the growth with the change below (replacing both patches).
> (although given the freeing of the old act_cookie pointer I wonder if
> this needs additional locking?)
>

I think we are safe. The cookie should not be touched by any datapath
code.

Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal