On Mon, 7 Nov 2016 19:49:03 +0100
Daniel Bristot de Oliveira [off-list ref] wrote:

On 11/07/2016 07:32 PM, Steven Rostedt wrote:

quoted

quoted

Excellent this would improve the situation with deadlocks as a result of  

quoted

cgroup_locks not being released due to lack of workqueue processing.  

?? What deadlocks do you see? I mean, can you show the situation that
throttling RT tasks will cause deadlock?

Sorry, but I'm just not seeing it.  

It is not a deadlock in the theoretical sense of the word, but it is
more a side effect of the starvation - that looks like a deadlock.

There is a case where the removal of a cgroup dir calls
lru_add_drain_all(), that might schedule a kworker in the CPU that is
running the spinning-rt task. The kworker will starve - because they are
SCHED_OTHER by design, the lru_add_drain_all() will wait forever while
holding the cgroup lock and this will cause a lot of problems on other
tasks.

I understand the issue with not throttling an RT task, but this patch
is about not not throttling! That is, what scenario is there that will
cause a "deadlock" or deadlock like to happen when we *do* throttle,
where not throttling will work better, as this patch would have?

-- Steve