Re: [RFC PATCH] mm/mmap: Fix uprobe anon page be overwritten when expanding vma during mremap

[Pu Lehui <pulehui@huaweicloud.com>]

On 2025/5/26 23:48, Oleg Nesterov wrote:
> Hi Lehui,
> 
> As I said, I don't understand mm/, so can't comment, but...
> 
> On 05/26, Pu Lehui wrote:
>>
>> To make things simpler, perhaps we could try post-processing, that is:
>>
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index 83e359754961..46a757fd26dc 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -240,6 +240,11 @@ static int move_ptes(struct pagetable_move_control
>> *pmc,
>>                  if (pte_none(ptep_get(old_pte)))
>>                          continue;
>>
>> +               /* skip move pte when expanded range has uprobe */
>> +               if (unlikely(pte_present(*new_pte) &&
>> +                            vma_has_uprobes(pmc->new, new_addr, new_addr +
>> PAGE_SIZE)))
>> +                       continue;
>> +
> 
> I was thinking about
> 
> 	WARN_ON(!pte_none(*new_pte))
> 
> at the start of the main loop.
> 
> Obviously not to fix the problem, but rather to make it more explicit.
> 
> This matches the similar xxx_none() checks in the move_pgt_entry() paths,
> say, move_normal_pmd().
> 
> Oleg.

Got it. It will help identify problems in time.