netdev - Re: [PATCH net] ipmr, ip6mr: fix scheduling while atomic and a deadlock with ipmr_get

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Message-Id: <20160925.234238.501504782961869524.davem@davemloft.net>
Date:   Sun, 25 Sep 2016 23:42:38 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     nikolay@...ulusnetworks.com
Cc:     netdev@...r.kernel.org, tgraf@...g.ch, roopa@...ulusnetworks.com,
        sharpd@...ulusnetworks.com
Subject: Re: [PATCH net] ipmr, ip6mr: fix scheduling while atomic and a
 deadlock with ipmr_get_route

From: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Date: Sun, 25 Sep 2016 23:08:31 +0200

> Since the commit below the ipmr/ip6mr rtnl_unicast() code uses the portid
> instead of the previous dst_pid which was copied from in_skb's portid.
> Since the skb is new the portid is 0 at that point so the packets are sent
> to the kernel and we get scheduling while atomic or a deadlock (depending
> on where it happens) by trying to acquire rtnl two times.
> Also since this is RTM_GETROUTE, it can be triggered by a normal user.
> 
> Here's the sleeping while atomic trace:
 ...
> Fixes: 2942e9005056 ("[RTNETLINK]: Use rtnl_unicast() for rtnetlink unicasts")
> Signed-off-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>

This approach looks fine to me, applied and queued up for -stable.