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 12:09:03PM +0200, David Hildenbrand wrote:
> > > > >    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". :)
> 
> :)
> 
> I would prefer to not make it okay to call mm_slot_entry() with a NULL
> pointer.

Maybe invert the checks then?

	if (!slot)
		goto unlock;
	mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
	if (ksm_scan.mm_slot == mm_slot)
		goto unlock;
	if (!mm_slot->rmap_list) {
	...

-- 
  Kiryl Shutsemau / Kirill A. Shutemov