Fix: Tests: race condition in test_event_tracker

Background
==========
The `test_event_tracker` file contains test cases when the event
generating app in executed in two distinct steps. Those two steps are
preparation and execution.
  1. the preparation is the launching the app in the background, and
  2. the execution is actually generating the event that should or
     should not be traced depending on the test case.

This is useful to test the tracker feature since we want to ensure that
already running apps are notified properly when changing their tracking
status.

Issue
=====
The `test_event_vpid_track_untrack` test case suffers from a race
condition that is easy to reproduce on Yocto.

The issue is that sometimes events are end up the trace when none is
expected.

This is due to the absence of synchronization point at the launch of the
app which leads to the app being scheduled in-between the track-untrack
calls leading to events being recorded to the trace.

It's easy to reproduce this issue on my machine by adding a `sleep 5`
between the track and untrack calls and setting the `NR_USEC_WAIT`
variable to 1.

Fix
===
Using the testapp `--sync-before-last-event-touch` flag to make the app
create a file when all but the last event are executed. We then have the
app wait until we create a file (`--sync-before-last-event`) to generate
that last event. This way, we are sure no event will be generated when
running the track and untrack commands.

Notes
=====
- This issue affects other test cases in this file.
- This commit fixes a typo in the test header.
- This commit adds `diag` calls to help tracking to what test the output
  relates to when reading the log.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ia2b68128dc9a805526f9748f31ec2c2d95566f31

diff --git a/tests/regression/tools/tracker/test_event_tracker b/tests/regression/tools/tracker/test_event_tracker
index feb3787155f8d74ca3914e6fdb80b49edb35c24d..cc0f698d2e45b05253889246ec07c1b28c551fbb 100755 (executable)
--- a/tests/regression/tools/tracker/test_event_tracker
+++ b/tests/regression/tools/tracker/test_event_tracker
@@ -5,7 +5,7 @@
 #
 # SPDX-License-Identifier: GPL-2.0-only
 
-TEST_DESC="LTTng - Event traker test"
+TEST_DESC="LTTng - Event tracker test"
 
 CURDIR=$(dirname "$0")/
 TESTDIR="$CURDIR/../../.."
@@ -15,7 +15,7 @@ TESTAPP_KERNEL_NAME="gen-kernel-test-events"
 TESTAPP_BIN="$TESTAPP_PATH/$TESTAPP_NAME/$TESTAPP_NAME"
 TESTAPP_KERNEL_BIN="$TESTAPP_PATH/$TESTAPP_KERNEL_NAME/$TESTAPP_KERNEL_NAME"
 SESSION_NAME="tracker"
-NR_ITER=100
+NR_ITER=1
 NUM_GLOBAL_TESTS=2
 NUM_UST_TESTS=283
 NUM_KERNEL_TESTS=462
@@ -30,27 +30,41 @@ SCRIPT_GROUPNAME="$(id -gn)"
 
 CHILD_PID=-1
 WAIT_PATH=
-AFTER_FIRST_PATH=
-BEFORE_LAST_PATH=
+TOUCH_BEFORE_LAST_PATH=
+SYNC_BEFORE_LAST_PATH=
 
 source $TESTDIR/utils/utils.sh
 
+# Launch the testapp and execute it up until right before the last event. It is
+# useful to do it in two seperate steps in order to test tracking and
+# untracking on an active app.
 function prepare_ust_app
 {
-       AFTER_FIRST_PATH=$(mktemp --tmpdir -u tmp.${FUNCNAME[0]}_sync_after_first.XXXXXX)
-       BEFORE_LAST_PATH=$(mktemp --tmpdir -u tmp.${FUNCNAME[0]}_sync_before_last.XXXXXX)
+       TOUCH_BEFORE_LAST_PATH=$(mktemp --tmpdir -u tmp.${FUNCNAME[0]}_touch_before_last.XXXXXX)
+       SYNC_BEFORE_LAST_PATH=$(mktemp --tmpdir -u tmp.${FUNCNAME[0]}_sync_before_last.XXXXXX)
+
+       $TESTAPP_BIN -i $NR_ITER -w $NR_USEC_WAIT \
+               --sync-before-last-event-touch "$TOUCH_BEFORE_LAST_PATH" \
+               --sync-before-last-event "$SYNC_BEFORE_LAST_PATH" &
 
-       $TESTAPP_BIN -i $NR_ITER -w $NR_USEC_WAIT -a "$AFTER_FIRST_PATH" -b "$BEFORE_LAST_PATH" &
        CHILD_PID=$!
+
+       # Wait for the app to execute all the way to right before the last
+       # event.
+       while [ ! -f "${TOUCH_BEFORE_LAST_PATH}" ]; do
+               sleep 0.5
+       done
 }
 
+# Generate the last event.
 function trace_ust_app
 {
-       touch "$BEFORE_LAST_PATH"
-       wait
+       # Ask the test app to generate the last event.
+       touch "$SYNC_BEFORE_LAST_PATH"
+       wait "$CHILD_PID"
        ok $? "Traced application stopped."
-       rm "$BEFORE_LAST_PATH"
-       rm "$AFTER_FIRST_PATH"
+       rm "$SYNC_BEFORE_LAST_PATH"
+       rm "$TOUCH_BEFORE_LAST_PATH"
 }
 
 function prepare_kernel_app
@@ -64,7 +78,7 @@ function prepare_kernel_app
 function trace_kernel_app
 {
        touch "$WAIT_PATH"
-       wait
+       wait "$CHILD_PID"
        ok $? "Traced application stopped."
        rm "$WAIT_PATH"
 }
@@ -78,6 +92,8 @@ function test_event_tracker()
        local tracker="$4"
        local channel=''
 
+       diag "${FUNCNAME[0]} $*"
+
        trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path"
@@ -117,6 +133,8 @@ function test_event_vpid_tracker()
        local wildcard="$3"
        local channel=''
 
+       diag "${FUNCNAME[0]} $*"
+
        trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path"
@@ -160,6 +178,8 @@ function test_event_pid_tracker()
        local wildcard="$3"
        local channel=''
 
+       diag "${FUNCNAME[0]} $*"
+
        trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path"
@@ -203,6 +223,8 @@ function test_event_tracker_fail()
        local wildcard="$2"
        local tracker="$3"
 
+       diag "${FUNCNAME[0]} $*"
+
        trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path"
@@ -222,6 +244,8 @@ function test_event_track_untrack()
        local tracker="$4"
        local channel=''
 
+       diag "${FUNCNAME[0]} $*"
+
        trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path"
@@ -262,6 +286,8 @@ function test_event_vpid_track_untrack()
        local wildcard="$3"
        local channel=''
 
+       diag "${FUNCNAME[0]} $*"
+
        trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path"
@@ -302,6 +328,8 @@ function test_event_pid_track_untrack()
        local wildcard="$3"
        local channel=''
 
+       diag "${FUNCNAME[0]} $*"
+
        trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path"
@@ -336,9 +364,9 @@ function test_event_pid_track_untrack()
 
 function test_event_ust_vpid_untrack_snapshot()
 {
-       local trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
+       diag "${FUNCNAME[0]} $*"
 
-       diag "Test_event_ust_vpid_untrack_snapshot"
+       local trace_path=$(mktemp --tmpdir -d tmp.${FUNCNAME[0]}_trace_path.XXXXXX)
 
        create_lttng_session_ok $SESSION_NAME "$trace_path" "--snapshot"