[PATCH 3/8] bdi: add a ->dev_name field to struct backing_dev_info

From: Christoph Hellwig
Date: Thu Apr 16 2020 - 03:17:06 EST


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@xxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
include/linux/backing-dev-defs.h | 1 +
mm/backing-dev.c | 13 ++++++++++---
2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 4fc87dee005a..249590bcccf7 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;
+ const char *dev_name;
struct device *owner;

struct timer_list laptop_mode_wb_timer;
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c2c44c89ee5d..4f6c05df72f9 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -938,9 +938,15 @@ 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);
- if (IS_ERR(dev))
+ bdi->dev_name = kvasprintf(GFP_KERNEL, fmt, args);
+ if (!bdi->dev_name)
+ return -ENOMEM;
+
+ dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
+ if (IS_ERR(dev)) {
+ kfree(bdi->dev_name);
return PTR_ERR(dev);
+ }

cgwb_bdi_register(bdi);
bdi->dev = dev;
@@ -1034,6 +1040,7 @@ static void release_bdi(struct kref *ref)
WARN_ON_ONCE(bdi->dev);
wb_exit(&bdi->wb);
cgwb_bdi_exit(bdi);
+ kfree(bdi->dev_name);
kfree(bdi);
}

@@ -1047,7 +1054,7 @@ 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);

--
2.25.1