linux-kernel - Re: [PATCH 1/1] veth: don't free priv->status until dev->destructor (v2)

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Message-ID: <m1zlaeu5jk.fsf@fess.ebiederm.org>
Date:	Tue, 04 Aug 2009 23:40:47 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Sachin Sant <sachinp@...ibm.com>,
	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>, matthltc@...ibm.com,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] veth: don't free priv->status until dev->destructor (v2)

Stephen Hemminger <shemminger@...tta.com> writes:

> On Fri, 26 Jun 2009 11:24:18 -0500
> "Serge E. Hallyn" <serue@...ibm.com> wrote:
>
>> Based on the commit msg on ae0e8e82205c903978a79ebf5e31c670b61fa5b4, it looks
>
>>  	ether_setup(dev);
>> @@ -306,7 +320,7 @@ static void veth_setup(struct net_device *dev)
>>  	dev->netdev_ops = &veth_netdev_ops;
>>  	dev->ethtool_ops = &veth_ethtool_ops;
>>  	dev->features |= NETIF_F_LLTX;
>> -	dev->destructor = free_netdev;
>> +	dev->destructor = veth_dev_free;
>>
>
> This is still going to oops if sysfs statistics referenced
> after module unload because module is unloaded (code is gone)
> and veth_dev_free no longer exists.

Has anyone actually seen that cause an oops?

The reason I am asking is that as I read the code we cannot have
this problem.  At worst the destructor callback is delayed until:

veth_exit
  rtnl_link_unregister
    rtnl_unlock
      netdev_run_todo
        dev->destructor


Similarly even if the sysfs filehandle is open we have called:

netdev_unregister_kobject
  ...
    sysfs_addrm_finish
      sysfs_deactivate

Which guarantees that sysfs_get_active_two will fail and all
subsequent actions on that file will fail.

Eric
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