Messages in this thread |  | | Date | Tue, 4 Feb 2020 20:01:16 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu |
| |
On Mon, 3 Feb 2020 11:33:01 -0500 Joel Fernandes <joel@joelfernandes.org> wrote:
> > --- a/kernel/trace/trace.h > > +++ b/kernel/trace/trace.h > > @@ -950,22 +950,25 @@ extern void __trace_graph_return(struct trace_array *tr, > > unsigned long flags, int pc); > > > > #ifdef CONFIG_DYNAMIC_FTRACE > > -extern struct ftrace_hash *ftrace_graph_hash; > > +extern struct ftrace_hash __rcu *ftrace_graph_hash; > > extern struct ftrace_hash *ftrace_graph_notrace_hash; > > > > static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace) > > { > > unsigned long addr = trace->func; > > int ret = 0; > > + struct ftrace_hash *hash; > > > > preempt_disable_notrace(); > > > > - if (ftrace_hash_empty(ftrace_graph_hash)) { > > + hash = rcu_dereference_protected(ftrace_graph_hash, !preemptible()); > > I think you can use rcu_dereference_sched() here? That way no need to pass > !preemptible. > > A preempt-disabled section is an RCU "sched flavor" section. Flavors are > consolidated in the backend, but in the front end the dereference API still > do have flavors.
Unfortunately, doing it with rcu_dereference_sched() causes a lockdep splat :-P. This is because ftrace can execute when rcu is not "watching" and that will trigger a lockdep error. That means, this origin patch *is* correct. I'm re-applying this one.
-- Steve
|  |