Re: [PATCH v11 0/7] alloc_tag and module codetag section fixes

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

Hi Suren and Andrew


On 2026/9/30 10:39, Suren Baghdasaryan wrote:
> On Tue, Sep 29, 2026 at 8:44 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>>
>> On Tue, 29 Sep 2026 16:20:07 +0800 Hao Ge <hao.ge@linux.dev> wrote:
>>
>>> With profiling toggled off, the overflow check in
>>> reserve_module_tags() did not run, a module could load with more
>>> tags than the page flags can address, and re-enabling profiling
>>> then silently corrupted /proc/allocinfo. On overflow the fix shuts
>>> profiling down, releases the reservation and returns -EAGAIN, and
>>> the codetag section lands as regular module data in the same load,
>>> so the module loads without profiling.
>>>
>>> Review of the earlier series by Sashiko turned up more problems.
>>>
>>> One is a race. layout_sections() and move_module() both asked
>>> codetag_needs_module_section() where a codetag section goes, and
>>> mem_profiling_support can change between the two calls, for instance
>>> when another module load overflows the tag index and shuts profiling
>>> down. move_module() then copied the codetag section to offset 0 of
>>> its regular destination and clobbered the first section placed in
>>> that region.
>>>
>>> v7 reworks where codetag sections are allocated, on a prototype by
>>> Petr Pavlu [1]. The allocation runs before layout_sections() and the
>>> placement is decided in one step, so nothing re-asks the question
>>> and the race is gone. The retry is gone too, on -EAGAIN the section
>>> is laid out as regular module data right in the same load.
>>
>> Thanks.
>>
>> Seven patches, all cc:stable.  Why is a backport proposed?
>> Documentation/process/stable-kernel-rules.rst gives guidelines - does
>> this series meet them?  Does Suren have thoughts?

Thanks, I've just gone through this carefully.

> 
> I think vmalloc fix in patch#2 should be posted separately and clearly
> quialifies for backporting as if fixes issues Hao found at [1].

Agreed. Patch #2 was added to this patch series because vm_module_tags_populate
suffers from the same issue. If we want to be more conservative, I'd prefer to keep
vm_module_tags_populate as it was in V10:
https://lore.kernel.org/all/20260915070001.113559-3-hao.ge@linux.dev/

Then we can submit a fix for __GFP_NOFAIL retry loop in __vmalloc_area_node() as a hotfix together
with our new patch #2. While at it, we can also check if there are any unnecessary calls to
vunmap_range family functions that can be cleaned up now that patch #2 is applied.


> 
> The rest are also bug fixes but their size is concerning. I'll review
> them first before advising on which ones should be backported. Some
> fixes address issues that happen very rarely and if a fix is too
> complex it might make sense to leave it be or fix it some other way
> with less churn. Please give me a couple of days to review them. With
> the upcoming LPC I'm trying to multiplex between several projects.

Thanks, sorry for all the hassle on you folks.

Thanks
Best Regards
Hao

> 
> [1] https://lore.kernel.org/all/b8005c24-ecac-45c4-840a-fd282f9693b5@linux.dev/
> 
>>
>> Also, Sashiko has been busy again:
>>         https://sashiko.dev/#/patchset/20260929082014.160587-1-hao.ge@linux.dev