writeback: initialize inode members that track writeback history

inode struct members that track cgroup writeback information
should be reinitialized when inode gets allocated from
kmem_cache. Otherwise, their values remain and get used by the
new inode.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Fixes: d10c809 ("writeback: implement foreign cgroup inode bdi_writeback switching")
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 3d65ae4634ed8350aee98a4e6f4e41fe40c7d282)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

Author: Tahsin Erdogan

fs/inode.c

@@ -154,6 +154,12 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	inode->i_rdev = 0;
 	inode->dirtied_when = 0;
 
+#ifdef CONFIG_CGROUP_WRITEBACK
+	inode->i_wb_frn_winner = 0;
+	inode->i_wb_frn_avg_time = 0;
+	inode->i_wb_frn_history = 0;
+#endif
+
 	if (security_inode_alloc(inode))
 		goto out;
 	spin_lock_init(&inode->i_lock);