Messages in this thread | | | Date | Mon, 25 Jan 2010 17:14:16 -0500 | From | Masami Hiramatsu <> | Subject | Re: [RFC PATCH 03/10] ftrace: Drop the ftrace_profile_enabled checks in tracing hot path |
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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.
Thank you,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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