netdev - Re: A problem with "ip=..." ipconfig and Atheros alx driver.

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Message-ID: <419eea59adc7af954f98ac81ec41a7be9cc0d9bb.camel@sipsolutions.net>
Date:   Fri, 30 Apr 2021 14:08:32 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Nikolai Zhubr <zhubr.2@...il.com>,
        Chris Snook <chris.snook@...il.com>, netdev@...r.kernel.org,
        nic-devel@...lcomm.com
Subject: Re: A problem with "ip=..." ipconfig and Atheros alx driver.

Hi Nikolai,

Wow - old code. And yet I'm still even using the device. Time to replace
the system that has it ;-)

> Now, after debugging it a little bit more, I've apparently found the 
> root cause. One can see in net/ipv4/ipconfig.c that ic_open_devs() tries 
> to ensure carrier is physically present. But before opening device(s) 
> and starting wait for the carrier, it calls rtnl_lock(). Now in 
> ethernet/atheros/alx/main.c one can see that at opening, it first calls 
> netif_carrier_off() then schedules alx_link_check() to do actual work, 
> so carrier detection is supposed to happen a bit later. Now looking at 
> this alx_link_check() carefully, first thing is does is rtnl_lock(). 
> Bingo! Double-lock. Effectively actual carrier check in alx is therefore 
> delayed just until ic_open_devs() gave up waiting for it and called 
> rtnl_unlock(). Hence this delay and timeout.

Fun. But we can just do it synchronously?

https://p.sipsolutions.net/e4f076ed1b4c8a78.txt

johannes