netdev - Re: [regression] Kernel panic on resume from sleep

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Message-ID: <20210304095110.7830dce4@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 4 Mar 2021 09:51:10 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Zbynek Michl <zbynek.michl@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [regression] Kernel panic on resume from sleep

On Thu, 4 Mar 2021 13:50:01 +0100 Zbynek Michl wrote:
> Looks good so far, but need to wait some more time as the issue was irregular.
> 
> Do you have any explanation why the calls disorder caused the panic
> just occasionally?

Depends if kernel attempts to try to send a packet before __alx_open()
finishes. You can probably make it more likely by running trafgen, iperf
or such while suspending and resuming?

> Also, the same (wrong) order I can see in the 3.16 kernel code, but it
> has worked fine with this kernel in all cases. So what is different in
> 5.10?

At some point in between those versions the driver got modified to
allocate and free the NAPI structures dynamically.

I didn't look too closely to find out if things indeed worked 100%
correctly before, but now they will reliably crash on a NULL pointer
dereference if transmission comes before open is done.