Re: [PATCH] once: Fix panic when module unload

[Hannes Frederic Sowa]

Hello,

On Tue, Aug 3, 2021, at 04:11, Kefeng Wang wrote:
> Hi ALL, I don't know who maintain the lib/once.c, add Greg and Andrew too,
> 
> Hi David, I check the history, the lib/once.c is from net/core/utils.c 
> since
> 
> commit 46234253b9363894a254844a6550b4cc5f3edfe8
> Author: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
> Date:   Thu Oct 8 01:20:35 2015 +0200
> 
>      net: move net_get_random_once to lib
> 
> This bug is found in our product test, we want to make sure that whether 
> this solution
> 
> is correct or not, so could David or any others help to review this patch.
> 
> Many thinks.

Thanks for the patch.

I see that it got marked as not applicable for the net trees:
<https://patchwork.kernel.org/project/netdevbpf/patch/20210622022138.23048-1-wangkefeng.wang@xxxxxxxxxx/>

Back then I added this code via the net/ tree thus I think it should get
picked up nonetheless hopefully.

Regarding your patch, I think it mostly looks fine:

It might be worthwhile to increment the reference counter inside the
preempt disabled bracket in find_module_by_key (and thus also rename
that function to make this fact more clear).

The other option would be to use the macro DO_ONCE and always pass in
THIS_MODULE from there, increment its ref counter in once_disable_jump.
This might be more canonical.

Thanks and sorry for the delay,
Hannes