Re: mm: deadlock between get_online_cpus/pcpu_alloc

[Christoph Lameter]

On Thu, 9 Feb 2017, Thomas Gleixner wrote:

> And how does that solve the problem at hand? Not at all:
>
> CPU 0	     	  	    CPU 1
>
> for_each_online_cpu(cpu)
>  ==> cpu = 1
> 			    stop_machine()
> 			    set_cpu_online(1, false)
>  queue_work(cpu1)
>
> Thanks,

Well thats not how I remember stop_machine does work. Doesnt it stop the
processing on all cpus otherwise its not a real usable stop.

The stop_machine would need to ensure that all cpus cease processing
before proceeding.