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

[Wei Yang <richard.weiyang@gmail.com>]

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);
+			}
 		}
 	}
 	spin_unlock(&ksm_mmlist_lock);
-- 
2.34.1