linux-kernel - Re: [PATCH 0/3][RFC] tracing/kprobes: prevent jprobes from crashing function graph tracer

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Message-Id: <1256861174.26028.3261.camel@gandalf.stny.rr.com>
Date:	Thu, 29 Oct 2009 20:06:14 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
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

On Thu, 2009-10-29 at 19:22 -0400, Masami Hiramatsu wrote:
> Steven Rostedt wrote:

> >> 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 */
> }

Hmm, That looks like it can be quite a hack. We don't know at that
moment if the handler has been traced or not. We can't always do the
function graph logic.

-- Steve


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