Messages in this thread |  | | Date | Wed, 22 Aug 2018 21:39:33 -0400 | From | Steven Rostedt <> | Subject | Re: [BUGFIX PATCH] tracing/kprobes: Fix to check notrace function with correct range |
| |
On Thu, 23 Aug 2018 10:18:31 +0900 Masami Hiramatsu <mhiramat@kernel.org> wrote:
> On Wed, 22 Aug 2018 08:58:09 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > On Tue, 21 Aug 2018 09:42:49 -0400 > > Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > On Tue, 21 Aug 2018 22:04:57 +0900 > > > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > > > > > Fix within_notrace_func() to check notrace function correctly. > > > > > > > > Since the ftrace_location_range(start, end) function checks > > > > the range inclusively (start <= ftrace-loc <= end), the end > > > > address must not include the entry address of next function. > > > > > > > > However, within_notrace_func() uses kallsyms_lookup_size_offset() > > > > to get the function size and calculate the end address from > > > > adding the size to the entry address. This means the end address > > > > is the entry address of the next function. > > > > > > > > In the result, within_notrace_func() fails to find notrace > > > > function if the next function of the target function is > > > > ftraced. > > > > > > > > Let's subtract 1 from the end address so that ftrace_location_range() > > > > can check it correctly. > > > > > > > > Fixes: commit 45408c4f9250 ("tracing: kprobes: Prohibit probing on notrace function") > > > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > > > > Reported-by: Michael Rodin <michael@rodin.online> > > > > --- > > > > > > > > > > Applied. Thanks Masami! I'll start testing this and send it upstream > > > when it's finished. > > > > > > > Hmm, this fix shows the extent of not tracing functions with notrace > > attched much deeper. For one thing, we can't hook kprobes to the > > __schedule() function (which is now what all the main schedule > > functions call). One of my tests used this function to test kprobes and > > it failed. > > > > I'll push this to Linus, but I'm wondering if we want to perhaps add a > > white list of functions marked "notrace" but still kprobes can trace? > > Yes, that is what I'm thinking about. Maybe most of notrace function is > safe for kprobes (like __schedule()). And if it is really critical, those > functions must be marked by NOKPROBE_SYMBOL(). >
Correct. This notrace was added because we want to not trace any function call between preempt_schedule() and where NEED_RESCHED is cleared. Because the function tracer does a preempt_enable_notrace() which triggers the preempt_schedule() call again, and we can end up in a recursive loop. But that is fixed, but by tracing __schedule() we do a song and dance of calling preempt_schedule_notrace and makes the trace output weird.
See commit 499d79559ffe4.
-- Steve
|  |