netdev - Re: [PATCH net] packet: Do not call fanout

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Message-ID: <64b9aba2-71c7-6e69-630e-aba995306dbf@citrix.com>
Date:   Mon, 13 Feb 2017 14:50:30 +0000
From:   Anoob Soman <anoob.soman@...rix.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
CC:     <netdev@...r.kernel.org>, <davem@...emloft.net>
Subject: Re: [PATCH net] packet: Do not call fanout_release from atomic
 contexts

On 13/02/17 14:26, Eric Dumazet wrote:
> On Mon, 2017-02-13 at 13:28 +0000, Anoob Soman wrote:
>
>> Wouldn't it be easier to call synchronize_net(), before calling
>> fanout_release_data() and kfree(f).
>> The behavior, wrt synchronize_net, would be same as before and
>> fanout_release() will cleanup everything without leaving any residue.
> So we would require two synchronize_net() calls instead of one ?
>
> synchronize_net() is very expensive on some hosts, it is a big hammer.
>
>
>

Yes, one before fanout_release_data() (will be called only if 
fanout->sk_ref == 0) and one after fanout_release().

I understand synchronize_net() is expensive, but adding another 
synchronize_net(),  before fanout_release_data(), will be no different 
from what we have in the existing code.

I can also make sure second synchronize_net() doesn't get called again, 
if fanout_release() calls synchronize_net(), by making fanout_release() 
return something to indicate it has done synchronize_net().

Thanks,

Anoob.