On Mon, Nov 06, 2017 at 11:32:12AM +0100, Peter Zijlstra wrote: > On Fri, Nov 03, 2017 at 02:45:45PM +0000, James Morse wrote: > > Hi Thomas, Peter, > > > > I'm trying to work out what stops a thread being pre-empted and migrated > > between > > calling get_online_cpus() and put_online_cpus().
Nothing; why would you think it would? All those functions guarantee is that any CPU observed as being online says online (and its converse, that a CPU observed as being offline, says offline, although less people care about that one). That is; it serializes against CPU hotplug, nothing else.
