Messages in this thread | | | Date | Tue, 26 Jan 2010 01:41:55 +0100 | From | Frederic Weisbecker <> | Subject | Re: [RFC PATCH 03/10] ftrace: Drop the ftrace_profile_enabled checks in tracing hot path |
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On Mon, Jan 25, 2010 at 05:14:16PM -0500, Masami Hiramatsu wrote: > Frederic Weisbecker wrote: > > On Fri, Jan 22, 2010 at 07:34:51AM -0500, Mathieu Desnoyers wrote: > >> * Steven Rostedt (rostedt@goodmis.org) wrote: > >>> On Thu, 2010-01-21 at 23:09 -0500, Mathieu Desnoyers wrote: > >>>> * Steven Rostedt (rostedt@goodmis.org) wrote: > >>> > >>>>> Hmm, interesting. Maybe something like that might work. But what if > >>>>> CONFIG_PREEMPT is enabled but CONFIG_FREEZER is not? > >>>> > >>>> Then you may want to make the function tracer depend on CONFIG_FREEZER, > >>>> but maybe Masami has other ideas ? > >>> > >>> egad no! This is just to help add guarantees to those that use the > >>> function tracer that when the tracing is disabled, it is guaranteed that > >>> no more tracing will be called by the function tracer. Currently, > >>> nothing relies on this. But we may add cases that might need this. > >> > >> Yep, identifying tracer quiescent state can become handy. > >> > >>> > >>> In fact, only those that need this requirement would need to do this > >>> trick. Anyway, we could make those depend on CONFIG_FREEZER, but that > >>> just seems to be a strange dependency. > >> > >> This makes me wonder (question for Masami)... > >> > >> static int __kprobes check_safety(void) > >> { > >> int ret = 0; > >> #if defined(CONFIG_PREEMPT) && defined(CONFIG_FREEZER) > >> ret = freeze_processes(); > >> if (ret == 0) { > >> struct task_struct *p, *q; > >> do_each_thread(p, q) { > >> if (p != current && p->state == TASK_RUNNING && > >> p->pid != 0) { > >> printk("Check failed: %s is running\n",p->comm); > >> ret = -1; > >> goto loop_end; > >> } > >> } while_each_thread(p, q); > > > > > > > > How does that deal with kernel threads that don't freeze? > > Hmm, right. It can't handle non-freezable kernel threads. > > > Also freezing every processes seems a bit of a heavy thing for that. > > Looks like a synchronize_tasks() would be really useful. > > Sure :-) > Maybe, I'd better remove booster support on preemptive kernel until then.
I don't know as I haven't looked deeper into check_safety(), but does the fact we have non-freezable tasks break the assumptions that make kprobes booster safe? If so then yeah, may be deactivate it for now.
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