netdev - Re: [PATCH] [PATCH net] net: Do not hold the reference for the same sk_rx

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Message-ID: <20170316181839.GA61894@kevinmbp.test.hulu.com>
Date:   Thu, 16 Mar 2017 11:18:39 -0700
From:   Kaiwen Xu <kaiwen.xu@...u.com>
To:     Jakub Sitnicki <jkbs@...hat.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] [PATCH net] net: Do not hold the reference for the same
 sk_rx_dst.

On Thu, Mar 16, 2017 at 11:45:03AM +0100, Jakub Sitnicki wrote:
> On Thu, Mar 16, 2017 at 10:12 AM GMT, Kevin Xu wrote:
> > Do you mean the message looping endlessly?
> 
> No, the message is emitted just once. Around 100 seconds after
> destroying a few namespaces. Occurs not so often, maybe once per ten
> runs.
> 
> -Jakub
> 

I saw that happening from time to time during my test as well, I suspect
it was because some TCP sockets stays in either TCP_TIME_WAIT or
TCP_FIN_WAIT1. But eventually those sockets get destroyed and lo gets
deleted as well.

The patch was fixing an issue I am seeing, that the message gets looped
forever, and causing a deadlock on new network ns creation.

Kevin

> > If so, then I suppose it's a different bug.
> >
> > Kevin
> >
> >> On Mar 16, 2017, at 3:01 AM, Jakub Sitnicki <jkbs@...hat.com> wrote:
> >>
> >>> On Thu, Mar 16, 2017 at 08:08 AM GMT, Kevin Xu wrote:
> >>> In some rare cases, inet_sk_rx_dst_set() may be called multiple times
> >>> on the same dst, causing reference count leakage. Eventually, it
> >>> prevents net_device to be destroyed. The bug then manifested as
> >>>
> >>> unregister_netdevice: waiting for lo to become free. Usage count = 1
> >>>
> >>> in the kernel log, preventing new network namespace creation.
> >>>
> >>> The patch works around the issue by checking whether the socket already
> >>> has the same dst set.
> >>>
> >>> Signed-off-by: Kevin Xu <kaiwen.xu@...u.com>
> >>> ---
> >>
> >> FWIW, with this patch applied I'm still sometimes seeing:
> >>
> >> [  125.928095] unregister_netdevice: waiting for lo to become free. Usage count = 1
> >>
> >> -Jakub