[PATCH 4/9] bdi: add a ->dev_name field to struct backing_dev_info

[Christoph Hellwig]

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 <yuyu...@huawei.com>
Signed-off-by: Christoph Hellwig <h...@lst.de>
Reviewed-by: Jan Kara <j...@suse.cz>
Reviewed-by: Bart Van Assche <bvanass...@acm.org>
---
 include/linux/backing-dev-defs.h | 1 +
 mm/backing-dev.c                 | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 4fc87dee005ab..2849bdbb3acbe 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -220,6 +220,7 @@ 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 c2c44c89ee5d7..efc5b83acd2df 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -938,7 +938,8 @@ 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);
 
@@ -1047,7 +1048,7 @@ 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);
 
-- 
2.26.2