Messages in this thread | | | Date | Fri, 14 Jun 2013 10:25:16 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] tracing/uprobes: Support ftrace_event_file base multibuffer |
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On Fri, Jun 14, 2013 at 12:33:27PM -0400, Steven Rostedt wrote: > On Fri, 2013-06-14 at 09:21 -0700, Paul E. McKenney wrote: > > > > > > @@ -548,15 +556,35 @@ static void uprobe_trace_print(struct trace_uprobe *tu, > > > > > /* uprobe handler */ > > > > > static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs) > > > > > { > > > > > - if (!is_ret_probe(tu)) > > > > > - uprobe_trace_print(tu, 0, regs); > > > > > + struct ftrace_event_file **file; > > > > > + > > > > > + if (is_ret_probe(tu)) > > > > > + return 0; > > > > > + > > > > > + file = rcu_dereference_raw(tu->files); > > > > > > Why are you using rcu_dereference_raw() and not rcu_dereference(). The > > > _raw() is a bit special, and unless you know what you are doing with RCU > > > here, don't use it. > > > > > > As I see you using rcu_dereference_raw() all over this patch, along with > > > mutexes, I believe that you are not using RCU correctly here. > > > > If irqs and preempt are disabled, I suggest using rcu_dereference_sched(). > > That is what it is there for. ;-) > > I believe this just copied what kprobes did, where irqs and preemption > is disabled. I don't believe that these probes have that same luxury. > > But that begs the question. Should we convert the rcu_dereference_raw() > in the kprobe code to rcu_dereference_sched()?
It makes a lot of sense to me, at least assuming no issues with the interrupts being disabled, but the checks not spotting this. Here is the check:
preempt_count() != 0 || irqs_disabled()
(With additional elaboration for if lockdep is enabled.)
Thanx, Paul
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