Christoph Hellwig <hch@xxxxxx> writes:
> On Mon, May 18, 2020 at 07:54:54PM +0800, Ming Lei wrote:
>>
>> I guess I misunderstood your point, sorry for that.
>>
>> The requirement is just that the request needs to be allocated on one online
>> CPU after INACTIVE is set, and we can use a workqueue to do that.
>
> I've looked over the code again, and I'm really not sure why we need that.
> Presumable the CPU hotplug code ensures tasks don't get schedule on the
> CPU running the shutdown state machine, so if we just do a retry of the
> tag allocation we can assume we are on a different CPU now (Thomas,
> correct me if that assumption is wrong).
User space tasks are kicked away once the CPU is cleared in the active
set, which is the very first operation on unplug.
Unbound kthreads are handled the same way as user space tasks.
Per CPU kthreads can run until the CPU clears the online bit which is at
the very end of the unplug operation just before it dies.
Some of these kthreads are managed and stop earlier, e.g. workqueues.
Thanks,
tglx
