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

On 2021/8/3 17:59, Hannes Frederic Sowa wrote:

Hello,

On Tue, Aug 3, 2021, at 04:11, Kefeng Wang wrote:

quoted

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 [off-list ref]
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@huawei.com/>

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 for your replay.

Yes, that was my first thought, add THIS_MODULE to __do_once_done(),

I will change to this way to fix the issue.

Thanks and sorry for the delay,
Hannes
.