[BUG] perf probe can't insert return kprobe

[BUG] perf probe can't insert return kprobe

[Jiri Olsa]

hi,
I couldn't use following perf command to insert return probe:

  # perf probe -a fork_exit=do_fork%return
  Added new event:
  Failed to write event: Invalid argument
    Error: Failed to add events.


I'm pretty sure I used this command before, so seems like
it's broken. I can still use debugfs tracing interface to
do that:
  # echo 'r:do_fork_entry do_fork' > kprobe_events

I used Arnaldo's latest perf/core and FC20 kernel:

  # uname -a
  Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
  # ./perf version
  perf version 3.18.g6a7d78


thanks,
jirka

Re: [BUG] perf probe can't insert return kprobe

[Arnaldo Carvalho de Melo]

Em Fri, Jan 09, 2015 at 03:55:39PM +0100, Jiri Olsa escreveu:
> hi,
> I couldn't use following perf command to insert return probe:
> 
>   # perf probe -a fork_exit=do_fork%return
>   Added new event:
>   Failed to write event: Invalid argument
>     Error: Failed to add events.

Wonder if we have any way of forcing 'perf probe' to show what it will
feed the kernel, perhaps -v?

> 
> I'm pretty sure I used this command before, so seems like
> it's broken. I can still use debugfs tracing interface to
> do that:
>   # echo 'r:do_fork_entry do_fork' > kprobe_events
> 
> I used Arnaldo's latest perf/core and FC20 kernel:
> 
>   # uname -a
>   Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
>   # ./perf version
>   perf version 3.18.g6a7d78
> 
> 
> thanks,
> jirka

Re: [BUG] perf probe can't insert return kprobe

[David Ahern]

On 1/9/15 8:03 AM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Jan 09, 2015 at 03:55:39PM +0100, Jiri Olsa escreveu:
>> hi,
>> I couldn't use following perf command to insert return probe:
>>
>>    # perf probe -a fork_exit=do_fork%return
>>    Added new event:
>>    Failed to write event: Invalid argument
>>      Error: Failed to add events.
>
> Wonder if we have any way of forcing 'perf probe' to show what it will
> feed the kernel, perhaps -v?

# strace -e write perf probe -a fork_exit=do_fork%return
write(1, "Added new event:\n", 17Added new event:
)      = 17
write(3, "r:probe/fork_exit do_fork+0", 27) = 27

Would be nice to add the output to perf -v though.

David

Re: [BUG] perf probe can't insert return kprobe

[David Ahern]

On 1/9/15 7:55 AM, Jiri Olsa wrote:
> hi,
> I couldn't use following perf command to insert return probe:
>
>    # perf probe -a fork_exit=do_fork%return
>    Added new event:
>    Failed to write event: Invalid argument
>      Error: Failed to add events.
>
>
> I'm pretty sure I used this command before, so seems like
> it's broken. I can still use debugfs tracing interface to
> do that:
>    # echo 'r:do_fork_entry do_fork' > kprobe_events
>
> I used Arnaldo's latest perf/core and FC20 kernel:
>
>    # uname -a
>    Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
>    # ./perf version
>    perf version 3.18.g6a7d78
>

If you want to bisect it the perf-probe command works for me on FC20, 
3.17.7-200.fc20.x86_64 with perf from 3.12 (my local modified version is 
based on 3.12).

David

Re: [BUG] perf probe can't insert return kprobe

[Namhyung Kim]

On Fri, Jan 09, 2015 at 03:55:39PM +0100, Jiri Olsa wrote:
> hi,
> I couldn't use following perf command to insert return probe:
> 
>   # perf probe -a fork_exit=do_fork%return
>   Added new event:
>   Failed to write event: Invalid argument
>     Error: Failed to add events.
> 
> 
> I'm pretty sure I used this command before, so seems like
> it's broken. I can still use debugfs tracing interface to
> do that:
>   # echo 'r:do_fork_entry do_fork' > kprobe_events
> 
> I used Arnaldo's latest perf/core and FC20 kernel:
> 
>   # uname -a
>   Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
>   # ./perf version
>   perf version 3.18.g6a7d78
> 

Is it just return probe?  Did it work for normal kprobes?
Maybe it's related to the below:

https://lkml.org/lkml/2014/12/31/15

Have you check the acme/perf/urgent too?

Thanks,
Namhyung

Re: [BUG] perf probe can't insert return kprobe

[David Ahern]

On 1/9/15 8:21 AM, Namhyung Kim wrote:
> Is it just return probe?  Did it work for normal kprobes?
> Maybe it's related to the below:
>
> https://lkml.org/lkml/2014/12/31/15
>
> Have you check the acme/perf/urgent too?

I believe that commit impacts uprobes only.

David

Re: [BUG] perf probe can't insert return kprobe

[Jiri Olsa]

On Sat, Jan 10, 2015 at 12:21:13AM +0900, Namhyung Kim wrote:
> On Fri, Jan 09, 2015 at 03:55:39PM +0100, Jiri Olsa wrote:
> > hi,
> > I couldn't use following perf command to insert return probe:
> > 
> >   # perf probe -a fork_exit=do_fork%return
> >   Added new event:
> >   Failed to write event: Invalid argument
> >     Error: Failed to add events.
> > 
> > 
> > I'm pretty sure I used this command before, so seems like
> > it's broken. I can still use debugfs tracing interface to
> > do that:
> >   # echo 'r:do_fork_entry do_fork' > kprobe_events
> > 
> > I used Arnaldo's latest perf/core and FC20 kernel:
> > 
> >   # uname -a
> >   Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
> >   # ./perf version
> >   perf version 3.18.g6a7d78
> > 
> 
> Is it just return probe?  Did it work for normal kprobes?

yep, works for normal probes

> Maybe it's related to the below:
> 
> https://lkml.org/lkml/2014/12/31/15
> 
> Have you check the acme/perf/urgent too?

hum.. can't access lkml, I'll check, also with perf/urgent

thanks,
jirka

Re: [BUG] perf probe can't insert return kprobe

[Jiri Olsa]

On Fri, Jan 09, 2015 at 04:30:56PM +0100, Jiri Olsa wrote:
> On Sat, Jan 10, 2015 at 12:21:13AM +0900, Namhyung Kim wrote:
> > On Fri, Jan 09, 2015 at 03:55:39PM +0100, Jiri Olsa wrote:
> > > hi,
> > > I couldn't use following perf command to insert return probe:
> > > 
> > >   # perf probe -a fork_exit=do_fork%return
> > >   Added new event:
> > >   Failed to write event: Invalid argument
> > >     Error: Failed to add events.
> > > 
> > > 
> > > I'm pretty sure I used this command before, so seems like
> > > it's broken. I can still use debugfs tracing interface to
> > > do that:
> > >   # echo 'r:do_fork_entry do_fork' > kprobe_events
> > > 
> > > I used Arnaldo's latest perf/core and FC20 kernel:
> > > 
> > >   # uname -a
> > >   Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
> > >   # ./perf version
> > >   perf version 3.18.g6a7d78
> > > 
> > 
> > Is it just return probe?  Did it work for normal kprobes?
> 
> yep, works for normal probes
> 
> > Maybe it's related to the below:
> > 
> > https://lkml.org/lkml/2014/12/31/15
> > 
> > Have you check the acme/perf/urgent too?
> 
> hum.. can't access lkml, I'll check, also with perf/urgent

neither helped..

jirka

Re: [BUG] perf probe can't insert return kprobe

[Namhyung Kim]

Hi Jiri,

On Fri, Jan 09, 2015 at 04:44:21PM +0100, Jiri Olsa wrote:
> On Fri, Jan 09, 2015 at 04:30:56PM +0100, Jiri Olsa wrote:
> > On Sat, Jan 10, 2015 at 12:21:13AM +0900, Namhyung Kim wrote:
> > > On Fri, Jan 09, 2015 at 03:55:39PM +0100, Jiri Olsa wrote:
> > > > hi,
> > > > I couldn't use following perf command to insert return probe:
> > > > 
> > > >   # perf probe -a fork_exit=do_fork%return
> > > >   Added new event:
> > > >   Failed to write event: Invalid argument
> > > >     Error: Failed to add events.
> > > > 
> > > > 
> > > > I'm pretty sure I used this command before, so seems like
> > > > it's broken. I can still use debugfs tracing interface to
> > > > do that:
> > > >   # echo 'r:do_fork_entry do_fork' > kprobe_events
> > > > 
> > > > I used Arnaldo's latest perf/core and FC20 kernel:
> > > > 
> > > >   # uname -a
> > > >   Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
> > > >   # ./perf version
> > > >   perf version 3.18.g6a7d78
> > > > 
> > > 
> > > Is it just return probe?  Did it work for normal kprobes?
> > 
> > yep, works for normal probes
> > 
> > > Maybe it's related to the below:
> > > 
> > > https://lkml.org/lkml/2014/12/31/15
> > > 
> > > Have you check the acme/perf/urgent too?
> > 
> > hum.. can't access lkml, I'll check, also with perf/urgent
> 
> neither helped..

I think I've found the reason.

The commit dfef99cd0b2c ("perf probe: Use ref_reloc_sym based address
instead of the symbol name") converts kprobes to use ref_reloc_sym
(i.e. _stext) and offset instead of using symbol's name directly.  So
on my system, adding do_fork ends up with like below:

  $ sudo perf probe -v --add do_fork%return
  probe-definition(0): do_fork%return
  symbol:do_fork file:(null) line:0 offset:0 return:1 lazy:(null)
  0 arguments
  Looking at the vmlinux_path (7 entries long)
  Using /lib/modules/3.17.6-1-ARCH/build/vmlinux for symbols
  Could not open debuginfo. Try to use symbols.
  Opening /sys/kernel/debug/tracing/kprobe_events write=1
  Added new event:
  Writing event: r:probe/do_fork _stext+456136
  Failed to write event: Invalid argument
    Error: Failed to add events. Reason: Operation not permitted (Code: -1)
  

As you can see, the do_fork was translated to _stext+456136.  This was
because to support (local) symbols that have same name.  But the
problem is that kretprobe requires to be inserted at function start
point so it simply checks whether it's called with offset 0.  And if
not, it'll return with -EINVAL.  You can see it with dmesg.

  $ dmesg | tail -1
  [125621.764103] Return probe must be used without offset.

So we need to use the symbol name instead of ref_reloc_sym in case of
return probes.  During the tracking down, I found a couple of problems
in the code.  I'll send fixes soon.

Thanks,
Namhyung

Re: Re: [BUG] perf probe can't insert return kprobe

[Masami Hiramatsu]

(2015/01/10 18:51), Namhyung Kim wrote:
> Hi Jiri,
> 
> On Fri, Jan 09, 2015 at 04:44:21PM +0100, Jiri Olsa wrote:
>> On Fri, Jan 09, 2015 at 04:30:56PM +0100, Jiri Olsa wrote:
>>> On Sat, Jan 10, 2015 at 12:21:13AM +0900, Namhyung Kim wrote:
>>>> On Fri, Jan 09, 2015 at 03:55:39PM +0100, Jiri Olsa wrote:
>>>>> hi,
>>>>> I couldn't use following perf command to insert return probe:
>>>>>
>>>>>   # perf probe -a fork_exit=do_fork%return
>>>>>   Added new event:
>>>>>   Failed to write event: Invalid argument
>>>>>     Error: Failed to add events.
>>>>>
>>>>>
>>>>> I'm pretty sure I used this command before, so seems like
>>>>> it's broken. I can still use debugfs tracing interface to
>>>>> do that:
>>>>>   # echo 'r:do_fork_entry do_fork' > kprobe_events
>>>>>
>>>>> I used Arnaldo's latest perf/core and FC20 kernel:
>>>>>
>>>>>   # uname -a
>>>>>   Linux krava 3.17.7-200.fc20.x86_64 #1 SMP Wed Dec 17 03:35:33 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
>>>>>   # ./perf version
>>>>>   perf version 3.18.g6a7d78
>>>>>
>>>>
>>>> Is it just return probe?  Did it work for normal kprobes?
>>>
>>> yep, works for normal probes
>>>
>>>> Maybe it's related to the below:
>>>>
>>>> https://lkml.org/lkml/2014/12/31/15
>>>>
>>>> Have you check the acme/perf/urgent too?
>>>
>>> hum.. can't access lkml, I'll check, also with perf/urgent
>>
>> neither helped..
> 
> I think I've found the reason.
> 
> The commit dfef99cd0b2c ("perf probe: Use ref_reloc_sym based address
> instead of the symbol name") converts kprobes to use ref_reloc_sym
> (i.e. _stext) and offset instead of using symbol's name directly.  So
> on my system, adding do_fork ends up with like below:
> 
>   $ sudo perf probe -v --add do_fork%return
>   probe-definition(0): do_fork%return
>   symbol:do_fork file:(null) line:0 offset:0 return:1 lazy:(null)
>   0 arguments
>   Looking at the vmlinux_path (7 entries long)
>   Using /lib/modules/3.17.6-1-ARCH/build/vmlinux for symbols
>   Could not open debuginfo. Try to use symbols.
>   Opening /sys/kernel/debug/tracing/kprobe_events write=1
>   Added new event:
>   Writing event: r:probe/do_fork _stext+456136
>   Failed to write event: Invalid argument
>     Error: Failed to add events. Reason: Operation not permitted (Code: -1)
>   
> 
> As you can see, the do_fork was translated to _stext+456136.  This was
> because to support (local) symbols that have same name.  But the
> problem is that kretprobe requires to be inserted at function start
> point so it simply checks whether it's called with offset 0.  And if
> not, it'll return with -EINVAL.  You can see it with dmesg.
> 
>   $ dmesg | tail -1
>   [125621.764103] Return probe must be used without offset.
> 
> So we need to use the symbol name instead of ref_reloc_sym in case of
> return probes.  During the tracking down, I found a couple of problems
> in the code.  I'll send fixes soon.

Oops, thank you for analyzing the problem:) I've completely forgot about
return probes with KASLR. This also should be fixed in kprobe-tracer,
which should convert given _stext+offset to actual symbol in kernel.

Thanks,

> 
> Thanks,
> Namhyung
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com