netdev - Re: 4.4.103 linux kernel regression

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Date:   Sat, 23 Dec 2017 19:36:48 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Mathias Tillman <master.homer@...il.com>
Cc:     netdev@...r.kernel.org, stable@...r.kernel.org,
        xiyou.wangcong@...il.com, dsahern@...il.com,
        jeffy.chen@...k-chips.com, davem@...emloft.net
Subject: Re: 4.4.103 linux kernel regression

On 23.12.2017 16:52, Greg KH wrote:
> adding stable@ and netdev@
> 
> On Sat, Dec 23, 2017 at 10:49:27AM +0000, Mathias Tillman wrote:
>> Hi, I wanted to make you aware of a recent regression to the Linux kernel
>> introduced with commit 2417da3f4d6bc4fc6c77f613f0e2264090892aa5:
>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/net/ipv6?h=linux-4.4.y&id=2417da3f4d6bc4fc6c77f613f0e2264090892aa5
> 
> Is this issue also present in Linus's tree?
> 
>> I have reported it here:
>> https://bugzilla.kernel.org/show_bug.cgi?id=198189
> 
> Bugzilla doesn't work for networking bugs, nor stable stuff, just for a
> few subsystems, sorry.
> 
>> Basically, that commit causes an endless loop if, for some reason, not all
>> devices are unregistered in the rollback_registered_many function in
>> net/dev.c
>>
>> Decided to contact you directly since I have yet to receive any reply on
>> the bug report, and I wasn't entirely sure what the procedure was. Please
>> do let me know if I have to change anything in the report.
> 
> I can revert it, but it would be good to verify if this is an issue in
> the latest releases or not first.

Most likely bug fixed by that commit hid refcount leak for loopback device.

Mathias, please try debug patch from attachment.
It logs all refcount changes for loopback in non-host net namespace.
Hopefully log would will be tiny and show what is missing.

Looks like vsftpd creates and destroys empty net-ns, like "unshare -n true"

View attachment "net-debug-lo-refcnt" of type "text/plain" (1892 bytes)