[Bug runtime/18642] New: Probes not always invoked when probed functions are called

["izi.an.contact at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18642

            Bug ID: 18642
           Summary: Probes not always invoked when probed functions are
                    called
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: izi.an.contact at gmail dot com
  Target Milestone: ---

Created attachment 8421
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8421&action=edit
stap-report output

Systemtap probes are invoked only some of the time when the probed function is
called.

This happens in two scenarios which may or may not be related:

1. Scenario I:
System calls such as read, write or bind using probes syscall.* (e.g.:
syscall.read, syscall.write, syscall.bind) are not called consistently.

In contrast, when using process.syscall probe, the probes are called
consistently when the probed functions are called.

We can't understand the discrepancy between the probe types behavior.

2. Scenario II:
Probe for process creation using probe kernel.function("sys_execve") and user
space probes for the created process (and its subprocesses) are not called
consistently. In our system the created process is usually bash, and the user
space probes on bash -
probe process("/bin/bash").function("pre_process_line")
probe process("/bin/bash").function("read_command")

are not invoked either when process creation probe isn't invoked.

--

It is worth mentioning that in these scenarios we run systemtap over an lxc
container and all the relevant processes run in this container.

Attached is the output from stap-report. We run systemtap 2.7 over ubuntu
14.04.2 (kernel 3.13.0-24-generic).

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