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Date: Thu, 29 Oct 2009 19:22:19 -0400 From: Masami Hiramatsu <mhiramat@...hat.com> To: rostedt@...dmis.org CC: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...ux-foundation.org>, Frederic Weisbecker <fweisbec@...il.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Arnaldo Carvalho de Melo <acme@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Li Zefan <lizf@...fujitsu.com>, Lai Jiangshan <laijs@...fujitsu.com>, "David S. Miller" <davem@...emloft.net>, Stephen Hemminger <shemminger@...ux-foundation.org> Subject: Re: [PATCH 0/3][RFC] tracing/kprobes: prevent jprobes from crashing function graph tracer Steven Rostedt wrote: > On Thu, 2009-10-29 at 18:02 -0400, Masami Hiramatsu wrote:\ >>> The solution I am proposing with this patch set is to add a call in >>> ftrace that lets other code in the kernel permanently disable functions from >>> being traced by the function and function graph tracer. As a probe function >>> is registered with jprobes, it calls this new function and that entry >>> will be removed from being traced. >>> >>> I tested this with this patch series and it does solve the problem. >>> >>> Some issues though: >>> >>> 1) this only works when DYNAMIC_FTRACE is enabled. We can prevent >>> function graph tracing with jprobes when DYNAMIC_FTRACE is not >>> enabled through Kconfig dependencies. Or have the registering of >>> a jprobe permanently disable function graph tracing. >> >> IMHO, those *probe handler should be tagged as __kprobes and notrace. > > Yeah, I agree. But how do you guarantee that it does. If one forgets, > than we still have the issue. We can perhaps test to make sure the > function is in the kprobes section. But that does not mean they will not > be notraced. The __kprobes and notrace are no longer in the same set. > >> >>> 2) This also prevents the function tracer from being able to trace a >>> function probe, even though the function tracer is not at issue >>> with this bug. >> >> I think we can skip those user handlers, because those are irregular >> functions and user can control (enable/disable) it. > > True, but it may be nice to still trace them. Hm, in that case, I think we can change jprobe_return() to call f-g-tracer's return handler if needed as below; --- static inline jprobe_return(void) { implicit_function_return(); /* This executes f-g-tracer prologue */ __jprobe_return(); /* This should be notraced */ } --- Thank you, -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@...hat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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