Re: [PATCH] Revert mm/vmstat.c: fix vmstat_update() preemption BUG

[Steven Rostedt]

On Wed, Apr 11, 2018 at 09:07:30PM +0200, Sebastian Andrzej Siewior wrote:
> 
> This already happens:
> - vmstat_shepherd() does get_online_cpus() and within this block it does
>   queue_delayed_work_on(). So this has to wait until cpuhotplug
>   completed before it can schedule something and then it won't schedule
>   anything on the "off" CPU.

But can't we have something like this happen: ?

	CPU0			CPU1			CPU2
	----			----			----
 get_online_cpus()
 queue_work(vmstat_update, cpu1)
    wakeup(kworker/1)
			     High prio task running
 put_online_cpus()
 						     Shutdown CPU 1
			     migrate kworker/1
 schedule kworker/1
 (smp_processor_id() != 1)

-- Steve