[PATCH 3/3] mm: __first_valid_page skip over offline pages

[Michal Hocko <mhocko@kernel.org>]

From: Michal Hocko <mhocko@suse.com>

__first_valid_page skips over invalid pfns in the range but it might
still stumble over offline pages. At least start_isolate_page_range
will mark those set_migratetype_isolate. This doesn't represent
any immediate AFAICS because alloc_contig_range will fail to isolate
those pages but it relies on not fully initialized page which will
become a problem later when we stop associating offline pages to zones.
So this is more a preparatory patch than a fix.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/page_isolation.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 5092e4ef00c8..2b958f33a1eb 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -138,12 +138,18 @@ static inline struct page *
 __first_valid_page(unsigned long pfn, unsigned long nr_pages)
 {
 	int i;
-	for (i = 0; i < nr_pages; i++)
-		if (pfn_valid_within(pfn + i))
-			break;
-	if (unlikely(i == nr_pages))
-		return NULL;
-	return pfn_to_page(pfn + i);
+
+	for (i = 0; i < nr_pages; i++) {
+		struct page *page;
+
+		if (!pfn_valid_within(pfn + i))
+			continue;
+		page = pfn_to_page(pfn + i);
+		if (PageReserved(page))
+			continue;
+		return page;
+	}
+	return NULL;
 }
 
 /*
@@ -184,8 +190,12 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 undo:
 	for (pfn = start_pfn;
 	     pfn < undo_pfn;
-	     pfn += pageblock_nr_pages)
-		unset_migratetype_isolate(pfn_to_page(pfn), migratetype);
+	     pfn += pageblock_nr_pages) {
+		struct page *page = pfn_to_page(pfn);
+		if (PageReserved(page))
+			continue;
+		unset_migratetype_isolate(page, migratetype);
+	}
 
 	return -EBUSY;
 }
-- 
2.11.0