On Sun, May 21, 2017 at 08:31:47PM +0200, Thomas Gleixner wrote:

On Fri, 19 May 2017, Christoph Hellwig wrote:

quoted

-	/* Stabilize the cpumasks */
-	get_online_cpus();

How is that protected against physical CPU hotplug? Physical CPU hotplug
manipulates the present mask.

It does indeed seem to.  Documentation/core-api/cpu_hotplug.rst claims
there are no locking rules for manipulations of cpu_present_mask,
maybe it needs and update to mention get/put_online_cpus() ?

Or maybe I should just switch to possible_cpu mask here like a lot of
code seems to do to avoid the hot plug issues, but that might be a bit
of a waste.