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mm/ksm: get mm_slot by mm_slot_entry() when slot is !NULL

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.

Link: https://lkml.kernel.org/r/20250919071244.17020-1-richard.weiyang@gmail.com
Link: https://lkml.kernel.org/r/20250919071244.17020-2-richard.weiyang@gmail.com
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

authored by

Wei Yang and committed by
Andrew Morton 08498be4 3dfd02c9

+11 -9
+11 -9
mm/ksm.c
··· 2936 2936 2937 2937 spin_lock(&ksm_mmlist_lock); 2938 2938 slot = mm_slot_lookup(mm_slots_hash, mm); 2939 - mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); 2940 - if (mm_slot && ksm_scan.mm_slot != mm_slot) { 2941 - if (!mm_slot->rmap_list) { 2942 - hash_del(&slot->hash); 2943 - list_del(&slot->mm_node); 2944 - easy_to_free = 1; 2945 - } else { 2946 - list_move(&slot->mm_node, 2947 - &ksm_scan.mm_slot->slot.mm_node); 2939 + if (slot) { 2940 + mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); 2941 + if (ksm_scan.mm_slot != mm_slot) { 2942 + if (!mm_slot->rmap_list) { 2943 + hash_del(&slot->hash); 2944 + list_del(&slot->mm_node); 2945 + easy_to_free = 1; 2946 + } else { 2947 + list_move(&slot->mm_node, 2948 + &ksm_scan.mm_slot->slot.mm_node); 2949 + } 2948 2950 } 2949 2951 } 2950 2952 spin_unlock(&ksm_mmlist_lock);