Re: [PATCH v3 1/4] remoteproc: core: Move cdev add before device add

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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



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