Re: [RFC PATCH 3/3] alloc_tag: remove /proc/allocinfo outside of mod_lock

[Hao Ge]

Hi Suren

On 2026/8/15 14:51, Suren Baghdasaryan wrote:
> On Thu, Aug 13, 2026 at 2:34 AM Hao Ge <hao.ge@xxxxxxxxx> wrote:
>>
>> shutdown_mem_profiling() calls remove_proc_entry() from
>> reserve_module_tags(), which runs under mod_lock held for write.
>> remove_proc_entry() waits for readers, and a reader takes mod_lock for
>> read in allocinfo_start():
>>
>>   CPU0 (insmod)                      CPU1 (read /proc/allocinfo)
>>   ----------------                   ----------------------------
>>   reserve_module_tags()
>>     down_write(&mod_lock)  [held]
>>                                      use_pde()            [in_use++]
>>                                      allocinfo_start()
>>                                        down_read(&mod_lock)  <- blocks
>>     shutdown_mem_profiling()
>>       remove_proc_entry()
>>         wait for in_use == 0         <- blocks
> 
> Yes, this is indeed a possible race.
> 
>>
>> Move remove_proc_entry() to a workqueue.
>>
>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
> 
> I think all these issues were reported by Sashiko, so you should add a
> Reported-by tag.
> 

Right, I'll add them. Patches 1 and 3 will be resent as a standalone
two-patch series with the Reported-by tags included.
Thanks a lot for all the help on this series.

Thanks
Best Regards
Hao

>> Signed-off-by: Hao Ge <hao.ge@xxxxxxxxx>
> 
> LGTM
> 
>> ---
>>  mm/alloc_tag.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
>> index 7481180dadd2..b80f5a151f28 100644
>> --- a/mm/alloc_tag.c
>> +++ b/mm/alloc_tag.c
>> @@ -591,6 +591,13 @@ void pgalloc_tag_swap(struct folio *new, struct folio *old)
>>         put_page_tag_ref(handle_new);
>>  }
>>
>> +static void remove_allocinfo_file(struct work_struct *work)
>> +{
>> +       remove_proc_entry(ALLOCINFO_FILE_NAME, NULL);
>> +}
>> +
>> +static DECLARE_WORK(remove_allocinfo_work, remove_allocinfo_file);
>> +
>>  static void shutdown_mem_profiling(bool remove_file)
>>  {
>>         if (mem_alloc_profiling_enabled())
>> @@ -600,7 +607,7 @@ static void shutdown_mem_profiling(bool remove_file)
>>                 return;
>>
>>         if (remove_file)
>> -               remove_proc_entry(ALLOCINFO_FILE_NAME, NULL);
>> +               schedule_work(&remove_allocinfo_work);
>>         mem_profiling_support = false;
>>  }
>>
>> --
>> 2.25.1
>>