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SubjectRe: [RFC PATCH 03/10] ftrace: Drop the ftrace_profile_enabled checks in tracing hot path
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?

Also freezing every processes seems a bit of a heavy thing for that.
Looks like a synchronize_tasks() would be really useful.



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