Re: There is a Tasks RCU stall warning

[Steven Rostedt]

On Tue, 11 Apr 2017 17:34:47 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Tue, 11 Apr 2017 17:31:33 -0400
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> 
> > The thread gets created when I enable the benchmark tracepoint. It just
> > so happens that my test enables *all* tracepoints, which would of
> > course include this one as well.
> > 
> > I'll have to look at this code to see why it is getting missed.  
> 
> Yep, this thread never goes to sleep, but will call cond_resched()
> periodically. This keeps rcu_tasks() from finishing.
> 
> Should I add a direct "schedule()" in there instead of a
> cond_resched(), or do you think rcu_tasks should have cond_resched() be
> a quiescent state as well?

Actually, I believe this found a bug in my trace_event benchmark
thread. On a preempt kernel, cond_resched() is a nop and expects to
only be preempted. Calling schedule() directly should fix everything. I
shouldn't depend on cond_resched() here.

-- Steve