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:

quoted

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

quoted

If so, then I suppose it's a different bug.

Kevin

quoted

On Mar 16, 2017, at 3:01 AM, Jakub Sitnicki [off-list ref] wrote:

quoted

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 <redacted>
---

FWIW, with this patch applied I'm still sometimes seeing:

[  125.928095] unregister_netdevice: waiting for lo to become free. Usage count = 1

-Jakub