Re: [PATCH net-next v2 0/2] ptp: safely cleanup when unregistering a PTP clock

On Tue, Sep 16, 2025 at 10:35:30PM +0100, Russell King (Oracle) wrote:

(I'm assuming drivers/ptp/ patches go via net-next as there is no
git tree against the "PTP HARDWARE CLOCK SUPPORT" maintainers entry.)

The standard rule in the kernel for unregistering user visible devices
is to unpublish the userspace API before doing any shutdown of the
resources necessary for the operation of the device.

PTP has several issues in this area:

1. ptp_clock_unregister() cancells and destroys work while the PTP
   chardev is still published, which gives the opportunity for a
   precisely timed user API call to cause a driver to attempt to
   queue the aux work.

2. PTP pins are not cleaned up - if userspace has enabled PTP pins,
   e.g. for extts, drivers are forced to do cleanup before calling
   ptp_clock_unregister() to stop events being forwarded into the
   PTP layer. E.g mv88e6xxx cancells its internal tai_event_work
   to avoid calling into the PTP clock code with a stale ptp_clock
   pointer, but a badly timed userspace EXTTS enable will re-schedule
   the tai_event_work.

Thanks, Russell!

For the series:

Acked-by: Richard Cochran <richardcochran@gmail.com>