Messages in this thread | | | Subject | Re: [RFC 0/4] tracing,x86_64 - function/graph trace without mcount/-pg/framepointer | From | Steven Rostedt <> | Date | Thu, 03 Feb 2011 14:00:28 -0500 |
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On Thu, 2011-02-03 at 18:35 +0100, Frederic Weisbecker wrote:
> > ftrace could do that now, but it would require a separate handler. I > > would need to disable preemption before calling the module code function > > handler. > > Kprobes takes care of handlers from modules already. > I'm not sure we want that, it makes the tracing code more sensitive.
Masami,
I'm looking at the optimize code, particularly kprobes_optinsn_template_holder(), which looks to be the template that is called on optimized kprobes. I don't see where preemption or interrupts are disabled when a probe is called.
If modules can register probes, and we can call it in any arbitrary location of the kernel, then preemption must be disabled prior to calling the module code. Otherwise you risk crashing the system on module unload.
module: ------- register_kprobe(probe);
Core: ----- hit break point call probe
module: ------- in probe function preempted
module: ------- unregister_kprobe(probe); stop_machine(); <module unloaded>
Core: ----- module <zombie>: ---------------- gets CPU again executes module code that's been freed DEATH BY ZOMBIES
Maybe I missed something. But does the optimize kprobes disable preemption or interrupts before calling the optimized probe?
-- Steve
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