Re: [PATCH v2] tracing/osnoise: Array printk init and cleanup

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 29 May 2026 22:33:37 -0500
Crystal Wood <crwood@redhat.com> wrote:
> > > diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
> > > index 75678053b21c..bda1e0e0d2e1 100644
> > > --- a/kernel/trace/trace_osnoise.c
> > > +++ b/kernel/trace/trace_osnoise.c
> > > @@ -476,8 +476,11 @@ static void print_osnoise_headers(struct seq_file *s)
> > >  										\
> > >  	rcu_read_lock();							\
> > >  	list_for_each_entry_rcu(inst, &osnoise_instances, list) {		\
> > > +		if (trace_array_get(inst->tr) < 0)				\
> > > +			continue;						\
> > >  		buffer = inst->tr->array_buffer.buffer;				\
> > >  		trace_array_printk_buf(buffer, _THIS_IP_, msg);			\
> > > +		trace_array_put(inst->tr);					\
> > >  	}									\
> > >  	rcu_read_unlock();							\
> > >  	osnoise_data.tainted = true;						\  
> > 
> > OK, I'll prepare a v3.  
> 
> Many osnoise_taint() callers, as well as timerlat_dump_stack(), can have
> preemption disabled, so the mutex in trace_array_get() won't work.

Right. OK, so another solution is to simply call synchronize_rcu() instead
of the kvfree_rcu_mightsleep(inst);

	synchronize_rcu();
	kvfree(inst);

Then there should not be any race, because the rmdir will have to wait for
the synchronization before finishing. This isn't something people should be
running a lot of, so I don't think it would cause too much pain in waiting
to unregister the osnoise tracer.

-- Steve