On 6/14/2021 9:56 PM, Greg KH wrote:
On Mon, Jun 14, 2021 at 07:21:08PM -0700, Siddharth Gupta wrote:
When cdev_add is called after device_add has been called there is no way for the userspace to know about the addition of a cdev as cdev_add itself doesn't trigger a uevent notification, or for the kernel to know about the change to devt. This results in two problems:
- mknod is never called for the cdev and hence no cdev appears on devtmpfs.
- sysfs links to the new cdev are not established.
The cdev needs to be added and devt assigned before device_add() is called in order for the relevant sysfs and devtmpfs entries to be created and the uevent to be properly populated.
So this means no one ever ran this code on a system that used devtmpfs?
How was it ever tested?
My testing was done with toybox + Android's ueventd ramdisk. As I mentioned in the discussion, the race became evident recently. I will make sure to test all such changes without systemd/ueventd in the future.
Thanks, Sid