Re: [PATCH v2 0/2] alloc_tag: fix a leak and a deadlock around shutdown_mem_profiling()

[Hao Ge <hao.ge@linux.dev>]

Hi Andrew

On 2026/8/27 11:39, Andrew Morton wrote:
> On Mon, 17 Aug 2026 14:27:24 +0800 Hao Ge <hao.ge@linux.dev> wrote:
> 
>> Two fixes for issues reported by sashiko:
>>
>>   1. percpu counter leak on modules loaded after profiling is disabled.
>>   2. AB-BA deadlock between module load and /proc/allocinfo readers.
>>
> 
> Thanks.  AI review asked two questions.  One pertinent to your
> alterations and one pertinent to Suren ;)
> 
> 	https://sashiko.dev/#/patchset/20260817062726.106511-1-hao.ge@linux.dev
> 
> I'll queue the patchset for 7.3-rc1, with a note-to-self.

Thanks for the heads up on the sashiko review questions.

The question on patch 1 (codetag_load_module() error handling)
has two parts.

The lost error code issue is already fixed; I sent the patch and
you queued it. (Thanks).

For the rollback part:

I've also seen Sashiko flag this same issue on another of my patches.
At the moment this case can't actually happen, alloc_tag is our only
registered codetag type, and codetag_module_init() cleans up its cmod
from the idr on every failure path, so nothing gets left behind.

That said, if we ever add a second codetag type down the line, the problem
Sashiko spotted will become real. I will follow up later to refine this
logic and make it more robust.

The question on patch 2 (async /proc/allocinfo removal racing with
alloc_tag_init() failure):

When I first read it, I think the window is unreachable. It requires
alloc_tag_init() to fail after proc_create() succeeded, and a process
to open and read /proc/allocinfo in the gap between schedule_work()
and the work running on system_wq.

But CONFIG_MEM_ALLOC_PROFILING is a bool, so when enabled alloc_tag is
always built in and it cannot be a loadable module. Its module_init(alloc_tag_init)
runs inside do_initcalls(), before /init is exec'd. Failures inside
alloc_tag_init() are already very unlikely to happen. When the failure
happens, no normal userspace exists yet.

That said, I realised the fix would actually be quite simple, we could just
move proc_create() to the end of alloc_tag_init().
I am not entirely sure whether we should do this though.

Suren, what is your opinion?

Thanks
Best Regards
Hao