Re: [PATCH -next] uprobes: fix two zero old_folio bugs in __replace_page()

[Tong Tiangen <tongtiangen@huawei.com>]

在 2025/2/18 0:12, Oleg Nesterov 写道:
> Can't comment, my understanding of mm/ is not enough these days.
> 
> Just one question...
> 
> On 02/17, Tong Tiangen wrote:
>>
>> Fixes: 7396fa818d62 ("uprobes/core: Make background page replacement logic account for rss_stat counters")
>> Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
> 
> Are you sure this logic was wrong from the very beginning? Just curious.
> 
> Oleg.

Yes, i checked the original code logic, and the put_page() didn't take 
zero pages into account.

Add Morton,Peter and David for discussion.

Thanks,
Tong.

> 
>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>> ---
>>   kernel/events/uprobes.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
>> index 46ddf3a2334d..ff5694acfa68 100644
>> --- a/kernel/events/uprobes.c
>> +++ b/kernel/events/uprobes.c
>> @@ -213,7 +213,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>>   		dec_mm_counter(mm, MM_ANONPAGES);
>>   
>>   	if (!folio_test_anon(old_folio)) {
>> -		dec_mm_counter(mm, mm_counter_file(old_folio));
>> +		if (!is_zero_folio(old_folio))
>> +			dec_mm_counter(mm, mm_counter_file(old_folio));
>>   		inc_mm_counter(mm, MM_ANONPAGES);
>>   	}
>>   
>> @@ -227,7 +228,8 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>>   	if (!folio_mapped(old_folio))
>>   		folio_free_swap(old_folio);
>>   	page_vma_mapped_walk_done(&pvmw);
>> -	folio_put(old_folio);
>> +	if (!is_zero_folio(old_folio))
>> +		folio_put(old_folio);
>>   
>>   	err = 0;
>>    unlock:
>> -- 
>> 2.25.1
>>
> 
> 
> .