From cc4f11e69fd00c61c38619759b07d00631bda5ca Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Fri, 28 Dec 2018 00:39:05 -0800
Subject: [PATCH] mm: migrate: lock buffers before migrate_page_move_mapping()
Git-commit: cc4f11e69fd00c61c38619759b07d00631bda5ca
Patch-mainline: v4.21-rc1
References: bsc#1084216

Lock buffers before calling into migrate_page_move_mapping() so that that
function doesn't have to know about buffers (which is somewhat unexpected
anyway) and all the buffer head logic is in buffer_migrate_page().

Link: http://lkml.kernel.org/r/20181211172143.7358-3-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Jan Kara <jack@suse.cz>

---
 mm/migrate.c |   25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -743,24 +743,23 @@ int buffer_migrate_page(struct address_s
 {
 	struct buffer_head *bh, *head;
 	int rc;
+	int expected_count;
 
 	if (!page_has_buffers(page))
 		return migrate_page(mapping, newpage, page, mode);
 
-	head = page_buffers(page);
+	/* Check whether page does not have extra refs before we do more work */
+	expected_count = expected_page_refs(page);
+	if (page_count(page) != expected_count)
+		return -EAGAIN;
 
-	rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
+	head = page_buffers(page);
+	if (!buffer_migrate_lock_buffers(head, mode))
+		return -EAGAIN;
 
+	rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
 	if (rc != MIGRATEPAGE_SUCCESS)
-		return rc;
-
-	/*
-	 * In the async case, migrate_page_move_mapping locked the buffers
-	 * with an IRQ-safe spinlock held. In the sync case, the buffers
-	 * need to be locked now
-	 */
-	if (mode != MIGRATE_ASYNC)
-		BUG_ON(!buffer_migrate_lock_buffers(head, mode));
+		goto unlock_buffers;
 
 	ClearPagePrivate(page);
 	set_page_private(newpage, page_private(page));
@@ -782,6 +781,8 @@ int buffer_migrate_page(struct address_s
 	else
 		migrate_page_states(newpage, page);
 
+	rc = MIGRATEPAGE_SUCCESS;
+unlock_buffers:
 	bh = head;
 	do {
 		unlock_buffer(bh);
@@ -790,7 +791,7 @@ int buffer_migrate_page(struct address_s
 
 	} while (bh != head);
 
-	return MIGRATEPAGE_SUCCESS;
+	return rc;
 }
 EXPORT_SYMBOL(buffer_migrate_page);
 #endif