Re: [PATCH 1/2] workqueue: Move wq_update_unbound_numa() to the beginning of CPU_ONLINE

[Tejun Heo]

On Tue, Jun 21, 2016 at 07:42:31PM +0530, Gautham R Shenoy wrote:
> > Subject: [PATCH] sched: allow kthreads to fallback to online && !active cpus
> > 
> > During CPU hotplug, CPU_ONLINE callbacks are run while the CPU is
> > online but not active.  A CPU_ONLINE callback may create or bind a
> > kthread so that its cpus_allowed mask only allows the CPU which is
> > being brought online.  The kthread may start executing before the CPU
> > is made active and can end up in select_fallback_rq().
> > 
> > In such cases, the expected behavior is selecting the CPU which is
> > coming online; however, because select_fallback_rq() only chooses from
> > active CPUs, it determines that the task doesn't have any viable CPU
> > in its allowed mask and ends up overriding it to cpu_possible_mask.
> > 
> > CPU_ONLINE callbacks should be able to put kthreads on the CPU which
> > is coming online.  Update select_fallback_rq() so that it follows
> > cpu_online() rather than cpu_active() for kthreads.
> > 
> > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> > Reported-by: Gautham R Shenoy <ego@xxxxxxxxxxxxxxxxxx>
> 
> Hi Tejun,
> 
> This patch fixes the issue on POWER. I am able to see the worker
> threads of the unbound workqueues of the newly onlined node with this.
> 
> Tested-by: Gautham R. Shenoy <ego@xxxxxxxxxxxxxxxxxx>

Peter?

-- 
tejun