[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <4AEF4178.90907@redhat.com>
Date: Mon, 02 Nov 2009 15:30:48 -0500
From: Masami Hiramatsu <mhiramat@...hat.com>
To: Frederic Weisbecker <fweisbec@...il.com>
CC: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
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
Frederic Weisbecker wrote:
> On Mon, Nov 02, 2009 at 10:02:23AM -0500, Masami Hiramatsu wrote:
>> Frederic Weisbecker wrote:
>>> I'm not sure I've well understood how is performed the call to the jprobe
>>> handler.
>>> But if I understand well we have:
>>>
>>> func() {
>>> int3() {
>>> jprobe_handler() {
>>> (-)
>>> set ip after iret to user_handler()
>>> }
>>> }
>>> user_handler() {
>>> jprobe_return() {
>>> (+)
>>> int3() {
>>> set ip after iret to func+...()
>>> }
>>> |
>>> |
>>> |
>>> <--------------
>>> (execute the rest of func())
>>> }
>>>
>>> If we replace (-) with pause_graph_tracing() and (+) with
>>> unpause_graph_tracing(), this should do the trick...I hope.
>>
>> I'm not so sure about pause_graph_tracing(), however, it seems that
>> int3() and jprobe_handler() already pushed on the stack of the
>> func graph tracer at (-). If it's true, where are those entries
>> popped up?
>>
>
>
> pause_graph_tracing() will disable the tracing for the current task
> but it won't disable the address pop from stack.
>
> If the above jprobe scheme is right, the scenario will be:
>
> func() {
> /* push func ret */
> int3() {
> /* push do_trap ret */
> jprobe_handler() {
> /* push jprobe_handler ret */
> pause_graph_tracing();
> set ip after iret to user_handler()
> } /* pop jprobe_handler ret */
> } /* pop do_trap ret */
> user_handler() {
> jprobe_return() {
> unpause_graph_tracing()
> int3() {
> /* push do_trap ret */
> set ip after iret to func+...()
> } /* pop do_trap ret */
> |
> |
> |
> <--------------
> (execute the rest of func())
> } /* pop func ret */
>
>
> Hmm?
Oh, I see. That should work. :-)
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/
Powered by blists - more mailing lists