From: Stephen Hemminger <stephen@networkplumber.org>
To: Henning Rogge <henning.rogge@fkie.fraunhofer.de>
Cc: <netdev@vger.kernel.org>
Subject: Re: [rtnetlink] Potential bug in Linux (rt)netlink code
Date: Fri, 12 Oct 2018 11:51:59 -0700 [thread overview]
Message-ID: <20181012115159.7ead2f97@xeon-e3> (raw)
In-Reply-To: <4d7a11b7-1f43-5669-6f19-3c746cc88306@fkie.fraunhofer.de>
On Fri, 12 Oct 2018 09:30:40 +0200
Henning Rogge <henning.rogge@fkie.fraunhofer.de> wrote:
> Hi,
>
> I am working on a self-written routing agent
> (https://github.com/OLSR/OONF) and am stuck on a problem with netlink
> that I cannot explain with an userspace error.
>
> I am using a netlink socket for setting routes
> (RTM_NEWROUTE/RTM_DELROUTE), querying the kernel for the current routes
> in the database (via a RTM_GETROUTE dump) and for getting multicast
> messages for ongoing routing changes.
>
> After a few netlink messages I get to the point where the kernel just
> does not responst to a RTM_NEWROUTE. No error, no answer, despite the
> NLM_F_ACK flag set)... but sometime when (during shutdown of the routing
> agent) the program sends another route command (most times a
> RTM_DELROUTE) I get a single netlink packet with a "successful" response
> for both the "missing" RTM_NEWROUTE and one for the new RTM DELROUTE
> sequence number.
>
> I am testing two routing agents, each of them in a systemd-nspawn based
> container connected over a bridge on the host system on a current Debian
> Testing (kernel 4.18.0-1-amd64).
>
> I am directly using the netlink sockets, without any other userspace
> library in between.
>
> I have checked the hexdumps of a couple of netlink messages (including
> the ones just before the bug happens) by hand and they seem to be okay.
>
> When I tried to add a "netlink listener" socket for futher debugging (ip
> link add nlmon0 type nlmon) the problem vanished until I removed the
> listener socket again.
>
> Any ideas how to debug this problem? Unfortunately I have no short
> example program to trigger the bug... I have rarely seen the problem for
> years (once every couple of months), but until a few days ago I never
> managed to reproduce it.
>
> Henning Rogge
Are you reading the responses to your requests? If you don't read
the response, the socket will get flow blocked.
next prev parent reply other threads:[~2018-10-13 2:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-12 7:30 [rtnetlink] Potential bug in Linux (rt)netlink code Henning Rogge
2018-10-12 18:51 ` Stephen Hemminger [this message]
2018-10-15 5:25 ` Henning Rogge
2018-10-22 5:22 ` Henning Rogge
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