netdev - Re: Question regarding bond delete notifications

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Message-ID: <20140430063136.GA2917@minipsycho.orion>
Date:	Wed, 30 Apr 2014 08:31:36 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:	netdev <netdev@...r.kernel.org>, Thomas Graf <tgraf@...g.ch>,
	David Miller <davem@...emloft.net>, j.vosburgh@...il.com,
	vfalico@...il.com, andy@...yhouse.net
Subject: Re: Question regarding bond delete notifications

Sun, Apr 27, 2014 at 08:16:27AM CEST, roopa@...ulusnetworks.com wrote:
>Hello,
>
>I am seeing a problem with the order of rtnl link notifications
>during bond deletes.
>If i delete a bond without deleting its slaves, kernel sends a
>RTM_DELLINK during unregister_netdevice
>(in rollback_registered_many) and then calls bond_uninit (ndo_uninit).
>bond_uninit inturn cleans up the slaves and generates a few
>RTM_NEWLINK rtnl notifications for NETDEV_CHANGEADDR and
>NETDEV_FEAT_CHANGE for the bond device.
>
>This is confusing to userspace listening for rtnl LINK Notifications.
>For example, libnl gets confused with RTM_NEWLINK arriving after
>RTM_DELLINK.
>The RTM_NEWLINK makes libnl believe that this is a new bond link. But
>kernel has already deleted the bond device.
>
>It seems like the kernel should  generate RTM_DELLINK notification
>after ndo_uninit. something like below.
>But am not sure if this change is safe for other netdevices.
>
>Is this a known problem ?. Any suggestions ?
>
>Thanks,
>Roopa
>
>diff --git a/net/core/dev.c b/net/core/dev.c
>index b1b0c8d..85cb73a 100644
>--- a/net/core/dev.c
>+++ b/net/core/dev.c
>@@ -5568,33 +5568,33 @@ static void rollback_registered_many(struct
>list_head *head)
>    list_for_each_entry(dev, head, unreg_list) {
>        /* Shutdown queueing discipline. */
>        dev_shutdown(dev);
>
>
>        /* Notify protocols, that we are about to destroy
>           this device. They should clean all the things.
>        */
>        call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
>
>-       if (!dev->rtnl_link_ops ||
>-           dev->rtnl_link_state == RTNL_LINK_INITIALIZED)
>-           rtmsg_ifinfo(RTM_DELLINK, dev, ~0U, GFP_KERNEL);
>-
>        /*
>         *  Flush the unicast and multicast chains
>         */
>        dev_uc_flush(dev);
>        dev_mc_flush(dev);
>
>        if (dev->netdev_ops->ndo_uninit)
>            dev->netdev_ops->ndo_uninit(dev);
>
>+       if (!dev->rtnl_link_ops ||
>+           dev->rtnl_link_state == RTNL_LINK_INITIALIZED)
>+           rtmsg_ifinfo(RTM_DELLINK, dev, ~0U, GFP_KERNEL);
>+
>        /* Notifier chain MUST detach us all upper devices. */
>        WARN_ON(netdev_has_any_upper_dev(dev));
>
>        /* Remove entries from kobject tree */
>        netdev_unregister_kobject(dev);
> #ifdef CONFIG_XPS
>        /* Remove XPS queueing entries */
>        netif_reset_xps_queues_gt(dev, 0);
> #endif
>    }
>


Now I cannot think about why this might troubles. But my feeling it this
might be problematic, just a feeling.

Your change seems logical though.
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