On Thu, 9 Feb 2017, Christoph Lameter wrote: > On Thu, 9 Feb 2017, Thomas Gleixner wrote: > > > > The stop_machine would need to ensure that all cpus cease processing > > > before proceeding. > > > > Ok. I try again: > > > > CPU 0 CPU 1 > > for_each_online_cpu(cpu) > > ==> cpu = 1 > > stop_machine() > > > > Stops processing on all CPUs by preempting the current execution and > > forcing them into a high priority busy loop with interrupts disabled. > > Exactly that means we are outside of the sections marked with > get_online_cpous(). > > > It does exactly what you describe. It stops processing on all other cpus > > until release, but that does not invalidate any data on those cpus. > > Why would it need to invalidate any data? The change of the cpu masks > would need to be done when the machine is stopped. This sounds exactly > like what we need and much of it is already there. You are just not getting it, really. The problem is that this for_each_online_cpu() is racy against a concurrent hot unplug and therefor can queue stuff for a not longer online cpu. That's what the mm folks tried to avoid by preventing a CPU hotplug operation before entering that loop. > Lets get rid of get_online_cpus() etc. And that solves what? Can you please start to understand the scope of the whole hotplug machinery including the requirements for get_online_cpus() before you waste everybodys time with your uninformed and halfbaken proposals? Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
