From c613fdc8d6231e1ba59a79168973ae43d4d3247a Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Mon, 4 May 2020 14:47:56 +0200
Subject: [PATCH] bdi: add a ->dev_name field to struct backing_dev_info

commit 6bd87eec23cbc9ed222bed0f5b5b02bf300e9a8d upstream.

Cache a copy of the name for the life time of the backing_dev_info
structure so that we can reference it even after unregistering.

Fixes: 68f23b89067f ("memcg: fix a crash in wb_workfn when a device disappears")
Reported-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 07e02d6df5ad..65d47522413c 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -197,6 +197,7 @@ struct backing_dev_info {
 	wait_queue_head_t wb_waitq;
 
 	struct device *dev;
+	char dev_name[64];
 	struct device *owner;
 
 	struct timer_list laptop_mode_wb_timer;
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 25234dd364d7..18ddd26967b6 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -881,7 +881,8 @@ int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
 	if (bdi->dev)	/* The driver needs to use separate queues per device */
 		return 0;
 
-	dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);
+	vsnprintf(bdi->dev_name, sizeof(bdi->dev_name), fmt, args);
+	dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
 	if (IS_ERR(dev))
 		return PTR_ERR(dev);
 
@@ -981,7 +982,7 @@ const char *bdi_dev_name(struct backing_dev_info *bdi)
 {
 	if (!bdi || !bdi->dev)
 		return bdi_unknown_name;
-	return dev_name(bdi->dev);
+	return bdi->dev_name;
 }
 EXPORT_SYMBOL_GPL(bdi_dev_name);
 
-- 
2.7.4