netdev - Re: [BUG] af_packet FANOUT and device dismantle

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Message-Id: <20160902.173730.771175006796901877.davem@davemloft.net>
Date:   Fri, 02 Sep 2016 17:37:30 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     netdev@...r.kernel.org
Subject: Re: [BUG] af_packet FANOUT and device dismantle

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 01 Sep 2016 17:04:43 -0700

> When you added fanout in commit dc99f600698dcac,
> it seems a device dismantle is not properly handled.
> 
> packet_notifier() does properly finds all sockets attached to the
> device and we call __unregister_prot_hook()
> 
> But the actual dev_remove_pack() is called when the last socket attached
> to the FANOUT group is _closed_ , possibly minutes after the device
> disappeared.
> 
> So we trigger the BUG_ON(!list_empty(&dev->ptype_all)); in
> netdev_run_todo(), that came with linux-4.0 in 
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7866a621043fbaca3d7389e9b9f69dd1a2e5a855
> 
> Fix would be to call dev_remote_pack() from __fanout_unlink() when
> num_members becomes 0.
> 
> Let me know if you agree with this, thanks.

I completely agree with your analysis, good catch.