Re: [Patch v3 1/2] mm/ksm: get mm_slot by mm_slot_entry() when slot is !NULL

[David Hildenbrand <david@redhat.com>]

On 24.09.25 11:35, Kiryl Shutsemau wrote:
> On Wed, Sep 24, 2025 at 12:48:53AM +0000, Wei Yang wrote:
>> Patch series "mm_slot: fix the usage of mm_slot_entry", v2.
>>
>> When using mm_slot in ksm, there is code like:
>>
>>       slot = mm_slot_lookup(mm_slots_hash, mm);
>>       mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
>>       if (mm_slot && ..) {
>>       }
>>
>> The mm_slot_entry() won't return a valid value if slot is NULL generally.
>> But currently it works since slot is the first element of struct
>> ksm_mm_slot.
>>
>> To reduce the ambiguity and make it robust, access mm_slot_entry() when
>> slot is !NULL.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Reviewed-by: Dev Jain <dev.jain@arm.com>
>> Reviewed-by: Lance Yang <lance.yang@linux.dev>
>> Cc: Kiryl Shutsemau <kirill@shutemov.name>
>> Cc: xu xin <xu.xin16@zte.com.cn>
>> Cc: Dan Carpenter <dan.carpenter@linaro.org>
>>
>> ---
>> v3:
>>    * fix uninitialized mm_slot
>> ---
>>   mm/ksm.c | 22 ++++++++++++----------
>>   1 file changed, 12 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/ksm.c b/mm/ksm.c
>> index 2dbe92e3dd52..c00a21800067 100644
>> --- a/mm/ksm.c
>> +++ b/mm/ksm.c
>> @@ -2921,7 +2921,7 @@ int __ksm_enter(struct mm_struct *mm)
>>   
>>   void __ksm_exit(struct mm_struct *mm)
>>   {
>> -	struct ksm_mm_slot *mm_slot;
>> +	struct ksm_mm_slot *mm_slot = NULL;
>>   	struct mm_slot *slot;
>>   	int easy_to_free = 0;
>>   
>> @@ -2936,15 +2936,17 @@ void __ksm_exit(struct mm_struct *mm)
>>   
>>   	spin_lock(&ksm_mmlist_lock);
>>   	slot = mm_slot_lookup(mm_slots_hash, mm);
>> -	mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
>> -	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
>> -		if (!mm_slot->rmap_list) {
>> -			hash_del(&slot->hash);
>> -			list_del(&slot->mm_node);
>> -			easy_to_free = 1;
>> -		} else {
>> -			list_move(&slot->mm_node,
>> -				  &ksm_scan.mm_slot->slot.mm_node);
>> +	if (slot) {
>> +		mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
>> +		if (ksm_scan.mm_slot != mm_slot) {
>> +			if (!mm_slot->rmap_list) {
>> +				hash_del(&slot->hash);
>> +				list_del(&slot->mm_node);
>> +				easy_to_free = 1;
>> +			} else {
>> +				list_move(&slot->mm_node,
>> +					  &ksm_scan.mm_slot->slot.mm_node);
>> +			}
> 
> Indent level gets extreme.

You call this extreme? :)

-- 
Cheers

David / dhildenb