mm,hwpoison: make get_hwpoison_page() call get_any_page()

__get_hwpoison_page() could fail to grab refcount by some race condition,
so it's helpful if we can handle it by retrying.  We already have retry
logic, so make get_hwpoison_page() call get_any_page() when called from
memory_failure().

As a result, get_hwpoison_page() can return negative values (i.e.  error
code), so some callers are also changed to handle error cases.
soft_offline_page() does nothing for -EBUSY because that's enough and
users in userspace can easily handle it.  unpoison_memory() is also
unchanged because it's broken and need thorough fixes (will be done
later).

Link: https://lkml.kernel.org/r/20210603233632.2964832-3-nao.horiguchi@gmail.comSigned-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -5938,6 +5938,8 @@ int get_hwpoison_huge_page(struct page *page, bool *hugetlb)
 		*hugetlb = true;
 		if (HPageFreed(page) || HPageMigratable(page))
 			ret = get_page_unless_zero(page);
+		else
+			ret = -EBUSY;
 	}
 	spin_unlock_irq(&hugetlb_lock);
 	return ret;

mm/memory-failure.c

@@ -1117,13 +1117,6 @@ static inline bool HWPoisonHandlable(struct page *page)
 	return PageLRU(page) || __PageMovable(page);
 }
 
-/**
- * __get_hwpoison_page() - Get refcount for memory error handling:
- * @page:	raw error page (hit by memory error)
- *
- * Return: return 0 if failed to grab the refcount, otherwise true (some
- * non-zero value.)
- */
 static int __get_hwpoison_page(struct page *page)
 {
 	struct page *head = compound_head(page);
@@ -1168,15 +1161,6 @@ static int __get_hwpoison_page(struct page *page)
 	return 0;
 }
 
-/*
- * Safely get reference count of an arbitrary page.
- *
- * Returns 0 for a free page, 1 for an in-use page,
- * -EIO for a page-type we cannot handle and -EBUSY if we raced with an
- * allocation.
- * We only incremented refcount in case the page was already in-use and it
- * is a known type we can handle.
- */
 static int get_any_page(struct page *p, unsigned long flags)
 {
 	int ret = 0, pass = 0;
@@ -1186,7 +1170,9 @@ static int get_any_page(struct page *p, unsigned long flags)
 		count_increased = true;
 
 try_again:
-	if (!count_increased && !__get_hwpoison_page(p)) {
+	if (!count_increased) {
+		ret = __get_hwpoison_page(p);
+		if (!ret) {
 			if (page_count(p)) {
 				/* We raced with an allocation, retry. */
 				if (pass++ < 3)
@@ -1198,7 +1184,15 @@ static int get_any_page(struct page *p, unsigned long flags)
 					goto try_again;
 				ret = -EIO;
 			}
-	} else {
+			goto out;
+		} else if (ret == -EBUSY) {
+			/* We raced with freeing huge page to buddy, retry. */
+			if (pass++ < 3)
+				goto try_again;
+			goto out;
+		}
+	}
+
 	if (PageHuge(p) || HWPoisonHandlable(p)) {
 		ret = 1;
 	} else {
@@ -1215,21 +1209,38 @@ static int get_any_page(struct page *p, unsigned long flags)
 		put_page(p);
 		ret = -EIO;
 	}
-	}
-
+out:
 	return ret;
 }
 
-static int get_hwpoison_page(struct page *p, unsigned long flags,
-			     enum mf_flags ctxt)
+/**
+ * get_hwpoison_page() - Get refcount for memory error handling
+ * @p:		Raw error page (hit by memory error)
+ * @flags:	Flags controlling behavior of error handling
+ *
+ * get_hwpoison_page() takes a page refcount of an error page to handle memory
+ * error on it, after checking that the error page is in a well-defined state
+ * (defined as a page-type we can successfully handle the memor error on it,
+ * such as LRU page and hugetlb page).
+ *
+ * Memory error handling could be triggered at any time on any type of page,
+ * so it's prone to race with typical memory management lifecycle (like
+ * allocation and free).  So to avoid such races, get_hwpoison_page() takes
+ * extra care for the error page's state (as done in __get_hwpoison_page()),
+ * and has some retry logic in get_any_page().
+ *
+ * Return: 0 on failure,
+ *         1 on success for in-use pages in a well-defined state,
+ *         -EIO for pages on which we can not handle memory errors,
+ *         -EBUSY when get_hwpoison_page() has raced with page lifecycle
+ *         operations like allocation and free.
+ */
+static int get_hwpoison_page(struct page *p, unsigned long flags)
 {
 	int ret;
 
 	zone_pcp_disable(page_zone(p));
-	if (ctxt == MF_SOFT_OFFLINE)
 	ret = get_any_page(p, flags);
-	else
-		ret = __get_hwpoison_page(p);
 	zone_pcp_enable(page_zone(p));
 
 	return ret;
@@ -1418,7 +1429,9 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
 
 	num_poisoned_pages_inc();
 
-	if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p, flags, 0)) {
+	if (!(flags & MF_COUNT_INCREASED)) {
+		res = get_hwpoison_page(p, flags);
+		if (!res) {
 			/*
 			 * Check "filter hit" and "race with other subpage."
 			 */
@@ -1439,6 +1452,10 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
 			}
 			action_result(pfn, MF_MSG_FREE_HUGE, res);
 			return res == MF_RECOVERED ? 0 : -EBUSY;
+		} else if (res < 0) {
+			action_result(pfn, MF_MSG_UNKNOWN, MF_IGNORED);
+			return -EBUSY;
+		}
 	}
 
 	lock_page(head);
@@ -1641,7 +1658,9 @@ int memory_failure(unsigned long pfn, int flags)
 	 * In fact it's dangerous to directly bump up page count from 0,
 	 * that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
 	 */
-	if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p, flags, 0)) {
+	if (!(flags & MF_COUNT_INCREASED)) {
+		res = get_hwpoison_page(p, flags);
+		if (!res) {
 			if (is_free_buddy_page(p)) {
 				if (take_page_off_buddy(p)) {
 					page_ref_inc(p);
@@ -1663,6 +1682,11 @@ int memory_failure(unsigned long pfn, int flags)
 				res = -EBUSY;
 			}
 			goto unlock_mutex;
+		} else if (res < 0) {
+			action_result(pfn, MF_MSG_UNKNOWN, MF_IGNORED);
+			res = -EBUSY;
+			goto unlock_mutex;
+		}
 	}
 
 	if (PageTransHuge(hpage)) {
@@ -1940,7 +1964,7 @@ int unpoison_memory(unsigned long pfn)
 		return 0;
 	}
 
-	if (!get_hwpoison_page(p, flags, 0)) {
+	if (!get_hwpoison_page(p, flags)) {
 		if (TestClearPageHWPoison(p))
 			num_poisoned_pages_dec();
 		unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
@@ -2156,7 +2180,7 @@ int soft_offline_page(unsigned long pfn, int flags)
 
 retry:
 	get_online_mems();
-	ret = get_hwpoison_page(page, flags, MF_SOFT_OFFLINE);
+	ret = get_hwpoison_page(page, flags);
 	put_online_mems();
 
 	if (ret > 0) {