Re: mm: deadlock between get_online_cpus/pcpu_alloc

[Thomas Gleixner]

On Tue, 7 Feb 2017, Christoph Lameter wrote:
> On Tue, 7 Feb 2017, Michal Hocko wrote:
> 
> > I am always nervous when seeing hotplug locks being used in low level
> > code. It has bitten us several times already and those deadlocks are
> > quite hard to spot when reviewing the code and very rare to hit so they
> > tend to live for a long time.
> 
> Yep. Hotplug events are pretty significant. Using stop_machine_XXXX() etc
> would be advisable and that would avoid the taking of locks and get rid of all the
> ocmplexity, reduce the code size and make the overall system much more
> reliable.

Huch? stop_machine() is horrible and heavy weight. Don't go there, there
must be simpler solutions than that.

Thanks,

	tglx