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

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

Hi Suren

On 2026/10/5 02:37, Suren Baghdasaryan wrote:
> On Wed, Sep 30, 2026 at 5:25 AM Hao Ge <hao.ge@linux.dev> wrote:
>>
>> 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/
> 
> I disagree with this approach. That means we are introducing an extra
> code inside vm_module_tags_populate() only to clean it up later.
> Instead please post Patch #2 separately. That posting should have your
> current patch that changes vmap_pages_xxx() to clean up on failure,
> followed by patch(es) which remove unnecessary cleanup that some
> functions currently perform by themselves. This patchset should
> definitely be tagged for stable.

You are right. Sorry for the confusion - my earlier deviation came
from not fully understanding the rules for getting patches into the
stable trees.

> Once that patchset is accepted, the rest of your current patchset
> fixing alloc_tags can be posted with correct assumption that
> vmap_pages_range() cleans up its partial mapping when it fails.
> 
> I know this sequence will take longer to upstream but I think it's the
> right way to go.

Make sense. Thanks for your continued support.

Best Regards
Hao

> 
>>
>> 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