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From: "mcermak at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sourceware.org
Subject: [Bug runtime/30131] Testcase at_var_timer_profile.exp regressed
Date: Fri, 17 Feb 2023 08:36:46 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D30131

--- Comment #1 from Martin Cermak <mcermak at redhat dot com> ---
Created attachment 14689
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D14689&action=3Ded=
it
a demo patch

My sense is that it might be a testcase problem:

> Here's the testcase script as of today:
> https://sourceware.org/git/?p=3Dsystemtap.git;a=3Dblob;f=3Dtestsuite/syst=
emtap.
> base/at_var_timer_profile.stp;h=3D479f74941a9fd739ea05b0d566c52d8929af7d0=
3;
> hb=3DHEAD

The testcase has two probes that fire asynchronously:

global active =3D 0

probe process.function("sub")
{
  active =3D 1
}

probe timer.profile {
  if (active && pid() =3D=3D target()) {
      printf("@var(\"foo\", @1)->bar: %d\n", @var("foo", @1)->bar);
      printf("@var(\"foo@at_var_timer_profile.c\", @1)->bar: %d\n",
             @var("foo@at_var_timer_profile.c", @1)->bar);
      printf("@var(\"foo@at_var_timer_profile.c\", @2)->bar: %d\n",
             @var("foo@at_var_timer_profile.c", @2)->bar);
      printf("@var(\"foo\", @1)$: %s\n", @var("foo", @1)$);
      printf("@var(\"foo\", @1)$$: %s\n", @var("foo", @1)$$);
      printf("@defined(@var(\"foo\", \"badmodle\")): %s\n",
             @defined(@var("foo", "badmodule")) ? "YES" : "NO")
      printf("@defined(@var(\"foo\", @3)): %s\n",
             @defined(@var("foo", @3)) ? "YES" : "NO")
      exit()
  }
}


The failure is caused by a fail to read variables that were available in the
first probe process.function (I've checked that), within the second probe -
timer.profile.  My hypothesis is that the second probe simply fires too lat=
e,
and the data are gone by then.  IMHO The mentioned kernel update possibly o=
nly
impacted the probe timing, indirectly causing this testcase failure. The
attached patch "fixes the failure" and demonstrates this hypothesis.

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