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

[Kiryl Shutsemau <kirill@shutemov.name>]

On Wed, Sep 24, 2025 at 11:40:21AM +0200, David Hildenbrand wrote:
> 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? :)

Emphasis on "gets". :)

-- 
  Kiryl Shutsemau / Kirill A. Shutemov