From: Jan Kara <jack@suse.cz>
Date: Wed, 16 Jan 2019 11:02:48 +0100
Subject: [PATCH] mm: migrate: Make buffer_migrate_page_norefs() actually succeed
References: bsc#1084216
Patch-mainline: v5.0-rc5
Git-commit: 80409c65e2c6cd1540045ee01fc55e50d95e0983

Currently, buffer_migrate_page_norefs() was constantly failing because
buffer_migrate_lock_buffers() grabbed reference on each buffer. In fact,
there's no reason for buffer_migrate_lock_buffers() to grab any buffer
references as the page is locked during all our operation and thus
nobody can reclaim buffers from the page. So remove grabbing of buffer
references which also makes buffer_migrate_page_norefs() succeed.

Fixes: 89cb0888ca14 "mm: migrate: provide buffer_migrate_page_norefs()"
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Jan Kara <jack@suse.cz>
---
 mm/migrate.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index a16b15090df3..712b231a7376 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -709,7 +709,6 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 	/* Simple case, sync compaction */
 	if (mode != MIGRATE_ASYNC) {
 		do {
-			get_bh(bh);
 			lock_buffer(bh);
 			bh = bh->b_this_page;
 
@@ -720,18 +719,15 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 
 	/* async case, we cannot block on lock_buffer so use trylock_buffer */
 	do {
-		get_bh(bh);
 		if (!trylock_buffer(bh)) {
 			/*
 			 * We failed to lock the buffer and cannot stall in
 			 * async migration. Release the taken locks
 			 */
 			struct buffer_head *failed_bh = bh;
-			put_bh(failed_bh);
 			bh = head;
 			while (bh != failed_bh) {
 				unlock_buffer(bh);
-				put_bh(bh);
 				bh = bh->b_this_page;
 			}
 			return false;
@@ -818,7 +814,6 @@ static int __buffer_migrate_page(struct address_space *mapping,
 	bh = head;
 	do {
 		unlock_buffer(bh);
-		put_bh(bh);
 		bh = bh->b_this_page;
 
 	} while (bh != head);
-- 
2.16.4