[PATCH 04/14] mm/ksm: add advance_scan_mm_slot() helper

[Longlong Xia]

From: Longlong Xia <xialonglong@xxxxxxxxxx>

Factor the four mm-slot cursor advances in scan_get_next_rmap_item()
and unmerge_and_remove_all_rmap_items() into a helper. Assert that
ksm_mmlist_lock is held.

No functional change intended.

Assisted-by: Zcode:GLM-5.3
Signed-off-by: Longlong Xia <xialonglong@xxxxxxxxxx>

---
 mm/ksm.c | 34 ++++++++++++++++++++--------------
 1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 18d037f571d3..aa33522627c7 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1119,6 +1119,22 @@ static inline void folio_set_stable_node(struct folio *folio,
 		   (void *)((unsigned long)stable_node | FOLIO_MAPPING_KSM));
 }
 
+/*
+ * Move the ksmd cursor onto the mm slot that follows @mm_slot in the
+ * ksm_mm_head list, and return the new cursor (@mm_slot may be
+ * &ksm_mm_head to (re)start from the first slot).  Called with
+ * ksm_mmlist_lock held.
+ */
+static struct ksm_mm_slot *advance_scan_mm_slot(struct ksm_mm_slot *mm_slot)
+{
+	struct mm_slot *slot;
+
+	lockdep_assert_held(&ksm_mmlist_lock);
+	slot = list_entry(mm_slot->slot.mm_node.next, struct mm_slot, mm_node);
+	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+	return ksm_scan.mm_slot;
+}
+
 #ifdef CONFIG_SYSFS
 /*
  * Only called through the sysfs control interface:
@@ -1215,15 +1231,12 @@ static int remove_all_stable_nodes(void)
 static int unmerge_and_remove_all_rmap_items(void)
 {
 	struct ksm_mm_slot *mm_slot;
-	struct mm_slot *slot;
 	struct mm_struct *mm;
 	struct vm_area_struct *vma;
 	int err = 0;
 
 	spin_lock(&ksm_mmlist_lock);
-	slot = list_entry(ksm_mm_head.slot.mm_node.next,
-			  struct mm_slot, mm_node);
-	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+	advance_scan_mm_slot(&ksm_mm_head);
 	spin_unlock(&ksm_mmlist_lock);
 
 	for (mm_slot = ksm_scan.mm_slot; mm_slot != &ksm_mm_head;
@@ -1253,9 +1266,7 @@ static int unmerge_and_remove_all_rmap_items(void)
 		mmap_read_unlock(mm);
 
 		spin_lock(&ksm_mmlist_lock);
-		slot = list_entry(mm_slot->slot.mm_node.next,
-				  struct mm_slot, mm_node);
-		ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+		advance_scan_mm_slot(mm_slot);
 		if (ksm_test_exit(mm)) {
 			mm_slot_remove(&mm_slot->slot);
 			spin_unlock(&ksm_mmlist_lock);
@@ -2662,10 +2673,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 			root_unstable_tree[nid] = RB_ROOT;
 
 		spin_lock(&ksm_mmlist_lock);
-		slot = list_entry(mm_slot->slot.mm_node.next,
-				  struct mm_slot, mm_node);
-		mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
-		ksm_scan.mm_slot = mm_slot;
+		mm_slot = advance_scan_mm_slot(mm_slot);
 		spin_unlock(&ksm_mmlist_lock);
 		/*
 		 * Although we tested list_empty() above, a racing __ksm_exit
@@ -2758,9 +2766,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 	remove_trailing_rmap_items(ksm_scan.rmap_list);
 
 	spin_lock(&ksm_mmlist_lock);
-	slot = list_entry(mm_slot->slot.mm_node.next,
-			  struct mm_slot, mm_node);
-	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+	advance_scan_mm_slot(mm_slot);
 	if (ksm_scan.address == 0) {
 		/*
 		 * We've completed a full scan of all vmas, holding mmap_lock
-- 
2.43.0