linux-kernel - Re: [PATCH] selftests/ftrace: Limit number of lines processed in 'trace'

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Date:   Wed, 19 Oct 2022 15:15:09 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Akanksha J N <akanksha@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH] selftests/ftrace: Limit number of lines processed in
 'trace'

Steven Rostedt wrote:
> On Wed, 19 Oct 2022 00:19:49 +0900
> Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> 
>> > You need to make sure that the "pause-on-trace" option is set or tracing_on
>> > is set to 0 (disabled). Otherwise, if the tracing is still active, then the
>> > reading of the trace file could potentially never end.  
>> 
>> initialize_ftrace() does this setting. So it must be set.
>> If you run the ftracetest on old kernel, this feature is not there and
>> it may cause a trouble. Naveen, can you clarify it?

Yes, the change to not pause on opening the trace file looks to be the 
problem.

> 
> But for old kernels that do not have "pause-on-trace" it should be the
> default. The "pause-on-trace" was added when the default was changed to not
> pause the trace while reading it.

It looks like the kernel patch was picked up, but Masami's patch for the 
selftest wasn't backported. I have requested a test with that applied.

Separately, before I saw your response, I came up with the below patch 
to update the selftests to disable tracing before reading the trace 
file. I have also requested this to be tested.


- Naveen

---
 .../selftests/ftrace/test.d/ftrace/fgraph-filter-stack.tc     | 4 +++-
 tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter.tc | 2 ++
 .../selftests/ftrace/test.d/ftrace/func-filter-notrace-pid.tc | 3 ++-
 .../testing/selftests/ftrace/test.d/ftrace/func-filter-pid.tc | 3 ++-
 4 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter-stack.tc b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter-stack.tc
index cf3ea42b12b09f..7e74df1ef928f9 100644
--- a/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter-stack.tc
+++ b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter-stack.tc
@@ -39,6 +39,7 @@ disable_tracing
 clear_trace
 enable_tracing
 sleep 1
+disable_tracing
 
 count=`cat trace | grep '()' | grep -v schedule | wc -l`
 
@@ -54,8 +55,9 @@ fi
 
 echo 0 > /proc/sys/kernel/stack_tracer_enabled
 clear_trace
+enable_tracing
 sleep 1
-
+disable_tracing
 
 count=`cat trace | grep '()' | grep -v schedule | wc -l`
 
diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter.tc b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter.tc
index b3ccdaec2a61ba..7e65a115054127 100644
--- a/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter.tc
+++ b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-filter.tc
@@ -24,6 +24,8 @@ fi
 echo function_graph > current_tracer
 enable_tracing
 sleep 1
+disable_tracing
+
 # search for functions (has "()" on the line), and make sure
 # that only the schedule function was found
 count=`cat trace | grep '()' | grep -v schedule | wc -l`
diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-notrace-pid.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-notrace-pid.tc
index 80541964b9270b..9fb0511b5d2eeb 100644
--- a/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-notrace-pid.tc
+++ b/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-notrace-pid.tc
@@ -51,6 +51,7 @@ do_test() {
 
     enable_tracing
     yield
+    disable_tracing
 
     count_pid=`cat trace | grep -v ^# | grep $PID | wc -l`
     count_other=`cat trace | grep -v ^# | grep -v $PID | wc -l`
@@ -60,7 +61,6 @@ do_test() {
 	fail "PID filtering not working? traced task = $count_pid; other tasks = $count_other "
     fi
 
-    disable_tracing
     clear_trace
 
     if [ $do_function_fork -eq 0 ]; then
@@ -77,6 +77,7 @@ do_test() {
 
     enable_tracing
     yield
+    disable_tracing
 
     count_pid=`cat trace | grep -v ^# | grep $PID | wc -l`
     count_other=`cat trace | grep -v ^# | grep -v $PID | wc -l`
diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-pid.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-pid.tc
index 2f7211254529ba..c55bcf2fe1966f 100644
--- a/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-pid.tc
+++ b/tools/testing/selftests/ftrace/test.d/ftrace/func-filter-pid.tc
@@ -51,6 +51,7 @@ do_test() {
 
     enable_tracing
     yield
+    disable_tracing
 
     count_pid=`cat trace | grep -v ^# | grep $PID | wc -l`
     count_other=`cat trace | grep -v ^# | grep -v $PID | wc -l`
@@ -60,7 +61,6 @@ do_test() {
 	fail "PID filtering not working?"
     fi
 
-    disable_tracing
     clear_trace
 
     if [ $do_function_fork -eq 0 ]; then
@@ -72,6 +72,7 @@ do_test() {
 
     enable_tracing
     yield
+    disable_tracing
 
     count_pid=`cat trace | grep -v ^# | grep $PID | wc -l`
     count_other=`cat trace | grep -v ^# | grep -v $PID | wc -l`