Re: [RFC PATCH 3/3 v0.2] sched/umcg: RFC: implement UMCG syscalls

On Thu, Jul 8, 2021 at 12:46 PM Peter Oskolkov [off-list ref] wrote:
[...]

Pretty much everything works, with one issue: when a worker
blocks, we need to wake its server in umcg_wq_worker_sleeping
called from sched_submit_work within preempt_disable block.
As the server_tid is set by the userspace, it can point to
a running/spinning task, and so wake_server will hang waiting
for ttwu() to succeed. I do not think this is appropriate,
but I am not sure at the moment how to resolve this. Any sugestions?

[...]

I think I can solve this by carefully ordering state changes (both
umcg state and task state) and maybe sending a signal to the wakee if
not enough. I'll try this approach in v0.3.