Re: [RFC PATCH 1/3] alloc_tag: skip percpu counter allocation when profiling is disabled

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

Hi Suren


On 2026/8/15 14:15, Suren Baghdasaryan wrote:
> On Thu, Aug 13, 2026 at 2:34 AM Hao Ge <hao.ge@linux.dev> wrote:
>>
>> After shutdown_mem_profiling() clears mem_profiling_support,
>> needs_section_mem() returns false, so later modules have their codetag
>> section placed as regular data and never enter the alloc_tag maple tree.
>> codetag_load_module() still called load_module(), which allocated a percpu
>> counter for every tag; release_module_tags() could not find these modules
>> on unload, so the counters leaked.
>>
>> Return CODETAG_MODULE_EXCLUDED from load_module() when profiling is off:
>> codetag_module_init() drops the module's cmod and no counters are
>> allocated. codetag_unload_module() now always calls free_section_mem(),
>> since an excluded module may still hold a reserved section.
>>
>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
>> Signed-off-by: Hao Ge <hao.ge@linux.dev>
> 
> Thanks for the fix. I think it could be done simpler, see below.

Agree, will do in the next version.

> 
>> ---
>>  include/linux/codetag.h | 4 ++++
>>  lib/codetag.c           | 8 +++++---
>>  mm/alloc_tag.c          | 8 ++++++--
>>  3 files changed, 15 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/codetag.h b/include/linux/codetag.h
>> index a25a085c2df1..88081c618673 100644
>> --- a/include/linux/codetag.h
>> +++ b/include/linux/codetag.h
>> @@ -52,6 +52,10 @@ struct codetag_type_desc {
>>  #endif
>>  };
>>
>> +/* module_load() return values */
>> +#define CODETAG_MODULE_LOAD    0       /* module loads with its tags */
>> +#define CODETAG_MODULE_EXCLUDED        1       /* module loads without its tags */
> 
> I see no reason for adding these special values. You could simply
> return -ENOTSUP when profiling is disabled.
> 
>> +
>>  struct codetag_iterator {
>>         struct codetag_type *cttype;
>>         struct codetag_module *cmod;
>> diff --git a/lib/codetag.c b/lib/codetag.c
>> index a9cda4c962a3..8506ecab9ea7 100644
>> --- a/lib/codetag.c
>> +++ b/lib/codetag.c
>> @@ -238,9 +238,10 @@ static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
>>         }
>>         up_write(&cttype->mod_lock);
>>
>> -       if (err < 0) {
>> +       if (err) {
>> +               /* Error or excluded: cmod is dropped, free it. */
> 
> IIUC here you want to call kfree() if profiling got disabled. If you
> return -ENOTSUP instead of CODETAG_MODULE_EXCLUDED then this condition
> does not need to change.
> 
>>                 kfree(cmod);
>> -               return err;
>> +               return err < 0 ? err : 0;
> 
> Here you can do:
>                     if (err && err != -ENOTSUP)
>                             return err;
>                    return 0;
> 
>>         }
>>
>>         return 0;
>> @@ -388,7 +389,8 @@ void codetag_unload_module(struct module *mod)
>>                         ++cttype->content_id;
>>                 }
>>                 up_write(&cttype->mod_lock);
>> -               if (found && cttype->desc.free_section_mem)
>> +               /* an excluded module may still hold section memory */
>> +               if (cttype->desc.free_section_mem)
>>                         cttype->desc.free_section_mem(mod, true);
>>         }
>>         mutex_unlock(&codetag_lock);
>> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
>> index 0a7b657fe2de..461fa87fbb0b 100644
>> --- a/mm/alloc_tag.c
>> +++ b/mm/alloc_tag.c
>> @@ -977,9 +977,13 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag
>>         struct alloc_tag *stop_tag;
>>         struct alloc_tag *tag;
>>
>> +       /* Profiling disabled: load the module but exclude its tags. */
>> +       if (!mem_profiling_support)
>> +               return CODETAG_MODULE_EXCLUDED;
> 
> Return -ENOTSUP here.
> 
> 
> 
>> +
>>         /* percpu counters for core allocations are already statically allocated */
>>         if (!mod)
>> -               return 0;
>> +               return CODETAG_MODULE_LOAD;
>>
>>         start_tag = ct_to_alloc_tag(start);
>>         stop_tag = ct_to_alloc_tag(stop);
>> @@ -1002,7 +1006,7 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag
>>                  */
>>                 kmemleak_ignore_percpu(tag->counters);
>>         }
>> -       return 0;
>> +       return CODETAG_MODULE_LOAD;
>>  }
>>
>>  static void replace_module(struct module *mod, struct module *new_mod)
>> --
>> 2.25.1
>>