[PATCH 5/6] page_isolation: Propagate temporary pageblock isolation error

[Gabriel Krisman Bertazi <krisman@collabora.com>]

If the page isolation failed because of racing the setup of the pages
migrate type, it is very likely that a further attempt will succeed. In
this case, instead of -EBUSY, return -EAGAIN, to let callers handle this
condition properly.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 mm/page_isolation.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index ce323e56b34d..a8169d8ea02d 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -30,10 +30,12 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
 	/*
 	 * We assume the caller intended to SET migrate type to isolate.
 	 * If it is already set, then someone else must have raced and
-	 * set it before us.  Return -EBUSY
+	 * set it before us.  Return -EAGAIN
 	 */
-	if (is_migrate_isolate_page(page))
+	if (is_migrate_isolate_page(page)) {
+		ret = -EAGAIN;
 		goto out;
+	}
 
 	pfn = page_to_pfn(page);
 	arg.start_pfn = pfn;
@@ -188,6 +190,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 	unsigned long pfn;
 	unsigned long undo_pfn;
 	struct page *page;
+	int ret = -EBUSY;
 
 	BUG_ON(!IS_ALIGNED(start_pfn, pageblock_nr_pages));
 	BUG_ON(!IS_ALIGNED(end_pfn, pageblock_nr_pages));
@@ -196,10 +199,13 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 	     pfn < end_pfn;
 	     pfn += pageblock_nr_pages) {
 		page = __first_valid_page(pfn, pageblock_nr_pages);
-		if (page &&
-		    set_migratetype_isolate(page, migratetype, flags)) {
-			undo_pfn = pfn;
-			goto undo;
+		if (page) {
+			ret = set_migratetype_isolate(page, migratetype,
+						      flags);
+			if (ret) {
+				undo_pfn = pfn;
+				goto undo;
+			}
 		}
 	}
 	return 0;
@@ -213,7 +219,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 		unset_migratetype_isolate(page, migratetype);
 	}
 
-	return -EBUSY;
+	return ret;
 }
 
 /*
-- 
2.20.1