[PATCH v4 1/2] mm/memory-failure: fix missing ->mf_stats count in hugetlb poison

[Jane Chu <jane.chu@oracle.com>]

When a newly poisoned subpage ends up in an already poisoned hugetlb
folio, 'num_poisoned_pages' is incremented, but the per node ->mf_stats
is not. Fix the inconsistency by designating action_result() to update
them both.

While at it, define __get_huge_page_for_hwpoison() return values in terms
of symbol names for better readibility. Also rename
folio_set_hugetlb_hwpoison() to hugetlb_update_hwpoison() since the
function does more than the conventional bit setting and the fact
three possible return values are expected.

Fixes: 18f41fa616ee4 ("mm: memory-failure: bump memory failure stats to pglist_data")
Cc: <stable@vger.kernel.org>
Signed-off-by: Jane Chu <jane.chu@oracle.com>
---
v3 -> v4:
  incorporate/adapt David's suggestions.
v2 -> v3:
  No change.
v1 -> v2:
  adapted David and Liam's comment, define __get_huge_page_for_hwpoison()
return values in terms of symbol names instead of naked integers for better
readibility.  #define instead of enum is used since the function has footprint
outside MF, just try to limit the MF specifics local.
  also renamed folio_set_hugetlb_hwpoison() to hugetlb_update_hwpoison()
since the function does more than the conventional bit setting and the
fact three possible return values are expected.
---
 mm/memory-failure.c | 75 +++++++++++++++++++++++++++------------------
 1 file changed, 45 insertions(+), 30 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index fbc5a01260c8..b3e27451d618 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1883,12 +1883,24 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
 	return count;
 }
 
-static int folio_set_hugetlb_hwpoison(struct folio *folio, struct page *page)
+#define	MF_HUGETLB_FOLIO_PRE_POISONED	3  /* folio already poisoned */
+#define	MF_HUGETLB_PAGE_PRE_POISON	4  /* exact page already poisoned */
+/*
+ * Set hugetlb folio as hwpoisoned, update folio private raw hwpoison list
+ * to keep track of the poisoned pages.
+ * Return:
+ *	0: folio was not already poisoned;
+ *	MF_HUGETLB_FOLIO_PRE_POISONED: folio was already poisoned: either
+ *		multiple pages being poisoned, or per page information unclear,
+ *	MF_HUGETLB_PAGE_PRE_POISON: folio was already poisoned, an exact
+ *		poisoned page is being consumed again.
+ */
+static int hugetlb_update_hwpoison(struct folio *folio, struct page *page)
 {
 	struct llist_head *head;
 	struct raw_hwp_page *raw_hwp;
 	struct raw_hwp_page *p;
-	int ret = folio_test_set_hwpoison(folio) ? -EHWPOISON : 0;
+	int ret = folio_test_set_hwpoison(folio) ? MF_HUGETLB_FOLIO_PRE_POISONED : 0;
 
 	/*
 	 * Once the hwpoison hugepage has lost reliable raw error info,
@@ -1896,20 +1908,17 @@ static int folio_set_hugetlb_hwpoison(struct folio *folio, struct page *page)
 	 * so skip to add additional raw error info.
 	 */
 	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
-		return -EHWPOISON;
+		return MF_HUGETLB_FOLIO_PRE_POISONED;
 	head = raw_hwp_list_head(folio);
 	llist_for_each_entry(p, head->first, node) {
 		if (p->page == page)
-			return -EHWPOISON;
+			return MF_HUGETLB_PAGE_PRE_POISON;
 	}
 
 	raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
 	if (raw_hwp) {
 		raw_hwp->page = page;
 		llist_add(&raw_hwp->node, head);
-		/* the first error event will be counted in action_result(). */
-		if (ret)
-			num_poisoned_pages_inc(page_to_pfn(page));
 	} else {
 		/*
 		 * Failed to save raw error info.  We no longer trace all
@@ -1955,44 +1964,43 @@ void folio_clear_hugetlb_hwpoison(struct folio *folio)
 	folio_free_raw_hwp(folio, true);
 }
 
+#define	MF_HUGETLB_FREED		0	/* freed hugepage */
+#define	MF_HUGETLB_IN_USED		1	/* in-use hugepage */
 /*
  * Called from hugetlb code with hugetlb_lock held.
- *
- * Return values:
- *   0             - free hugepage
- *   1             - in-use hugepage
- *   2             - not a hugepage
- *   -EBUSY        - the hugepage is busy (try to retry)
- *   -EHWPOISON    - the hugepage is already hwpoisoned
  */
 int __get_huge_page_for_hwpoison(unsigned long pfn, int flags,
 				 bool *migratable_cleared)
 {
 	struct page *page = pfn_to_page(pfn);
 	struct folio *folio = page_folio(page);
-	int ret = 2;	/* fallback to normal page handling */
+	int ret = -EINVAL;
 	bool count_increased = false;
+	int rc;
 
 	if (!folio_test_hugetlb(folio))
 		goto out;
 
 	if (flags & MF_COUNT_INCREASED) {
-		ret = 1;
+		ret = MF_HUGETLB_IN_USED;
 		count_increased = true;
 	} else if (folio_test_hugetlb_freed(folio)) {
-		ret = 0;
+		ret = MF_HUGETLB_FREED;
 	} else if (folio_test_hugetlb_migratable(folio)) {
-		ret = folio_try_get(folio);
-		if (ret)
+		if (folio_try_get(folio)) {
+			ret = MF_HUGETLB_IN_USED;
 			count_increased = true;
+		} else
+			ret = MF_HUGETLB_FREED;
 	} else {
 		ret = -EBUSY;
 		if (!(flags & MF_NO_RETRY))
 			goto out;
 	}
 
-	if (folio_set_hugetlb_hwpoison(folio, page)) {
-		ret = -EHWPOISON;
+	rc = hugetlb_update_hwpoison(folio, page);
+	if (rc >= MF_HUGETLB_FOLIO_PRE_POISONED) {
+		ret = rc;
 		goto out;
 	}
 
@@ -2029,22 +2037,29 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 	*hugetlb = 1;
 retry:
 	res = get_huge_page_for_hwpoison(pfn, flags, &migratable_cleared);
-	if (res == 2) { /* fallback to normal page handling */
+	switch (res) {
+	case -EINVAL:	/* fallback to normal page handling */
 		*hugetlb = 0;
 		return 0;
-	} else if (res == -EHWPOISON) {
-		if (flags & MF_ACTION_REQUIRED) {
-			folio = page_folio(p);
-			res = kill_accessing_process(current, folio_pfn(folio), flags);
-		}
-		action_result(pfn, MF_MSG_ALREADY_POISONED, MF_FAILED);
-		return res;
-	} else if (res == -EBUSY) {
+	case -EBUSY:
 		if (!(flags & MF_NO_RETRY)) {
 			flags |= MF_NO_RETRY;
 			goto retry;
 		}
 		return action_result(pfn, MF_MSG_GET_HWPOISON, MF_IGNORED);
+	case MF_HUGETLB_FOLIO_PRE_POISONED:
+	case MF_HUGETLB_PAGE_PRE_POISON:
+		if (flags & MF_ACTION_REQUIRED) {
+			folio = page_folio(p);
+			res = kill_accessing_process(current, folio_pfn(folio), flags);
+		}
+		if (res == MF_HUGETLB_FOLIO_PRE_POISONED)
+			action_result(pfn, MF_MSG_ALREADY_POISONED, MF_FAILED);
+		else
+			action_result(pfn, MF_MSG_HUGE, MF_FAILED);
+		return res;
+	default:
+		break;
 	}
 
 	folio = page_folio(p);
-- 
2.43.5