selftests/ftrace: Let fprobe test consider already enabled functions

The fprobe test fails on Fedora 41 since the fprobe test assumption that the number of enabled_functions is zero before the test starts is not necessarily true. Some user space tools, like systemd, add BPF programs that attach to functions. Those will show up in the enabled_functions table and must be taken into account by the fprobe test.

Therefore count the number of lines of enabled_functions before tests start, and use that as base when comparing expected results.

Fixes e85c5e9792b9 ("selftests/ftrace: Update fprobe test to check enabled_functions file")

Signed-off-by Heiko Carstens <[email protected]>

---
 .../test.d/dynevent/add_remove_fprobe.tc       | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

tools/testing/selftests/ftrace/test.d/dynevent/add_remove_fprobe.tc +11 -7

index 449f9d8be746..73f6c6fcecab 100644
@@ -10,12 +10,16 @@ PLACE=$FUNCTION_FORK
 PLACE2="kmem_cache_free"
 PLACE3="schedule_timeout"
 
+# Some functions may have BPF programs attached, therefore
+# count already enabled_functions before tests start
+ocnt=`cat enabled_functions | wc -l`
+
 echo "f:myevent1 $PLACE" >> dynamic_events
 
 # Make sure the event is attached and is the only one
 grep -q $PLACE enabled_functions
 cnt=`cat enabled_functions | wc -l`
-if [ $cnt -ne 1 ]; then
+if [ $cnt -ne $((ocnt + 1)) ]; then
 	exit_fail
 fi
 

@@ -23,7 +27,7 @@ echo "f:myevent2 $PLACE%return" >> dynamic_events
 
 # It should till be the only attached function
 cnt=`cat enabled_functions | wc -l`
-if [ $cnt -ne 1 ]; then
+if [ $cnt -ne $((ocnt + 1)) ]; then
 	exit_fail
 fi
 

@@ -32,7 +36,7 @@ echo "f:myevent3 $PLACE2" >> dynamic_events
 
 grep -q $PLACE2 enabled_functions
 cnt=`cat enabled_functions | wc -l`
-if [ $cnt -ne 2 ]; then
+if [ $cnt -ne $((ocnt + 2)) ]; then
 	exit_fail
 fi
 

@@ -49,7 +53,7 @@ grep -q myevent1 dynamic_events
 
 # should still have 2 left
 cnt=`cat enabled_functions | wc -l`
-if [ $cnt -ne 2 ]; then
+if [ $cnt -ne $((ocnt + 2)) ]; then
 	exit_fail
 fi
 

@@ -57,7 +61,7 @@ echo > dynamic_events
 
 # Should have none left
 cnt=`cat enabled_functions | wc -l`
-if [ $cnt -ne 0 ]; then
+if [ $cnt -ne $ocnt ]; then
 	exit_fail
 fi
 

@@ -65,7 +69,7 @@ echo "f:myevent4 $PLACE" >> dynamic_events
 
 # Should only have one enabled
 cnt=`cat enabled_functions | wc -l`
-if [ $cnt -ne 1 ]; then
+if [ $cnt -ne $((ocnt + 1)) ]; then
 	exit_fail
 fi
 

@@ -73,7 +77,7 @@ echo > dynamic_events
 
 # Should have none left
 cnt=`cat enabled_functions | wc -l`
-if [ $cnt -ne 0 ]; then
+if [ $cnt -ne $ocnt ]; then
 	exit_fail
 fi
 

Signature · 1 line

2.45.2

Quoted 5 lines · On Wed, 26 Feb 2025 15:27:03 +0100 Heiko Carstens <[email protected]> wrote:

The fprobe test fails on Fedora 41 since the fprobe test assumption that the number of enabled_functions is zero before the test starts is not necessarily true. Some user space tools, like systemd, add BPF programs that attach to functions. Those will show up in the enabled_functions table and must be taken into account by the fprobe test.

Hmm, this ftrace selftests has been expected to be run without any BPF programs... Is there any other issue on other test cases?

That is of course except for the "add/remove/test uprobe events" test where I sent a patch. Not sure what will happen with that one:

https://lore.kernel.org/all/[email protected]/

Hmm, this ftrace selftests has been expected to be run without any BPF programs... Is there any other issue on other test cases?

Quoted 2 lines · On Wed, 26 Feb 2025 23:54:47 +0900 Masami Hiramatsu (Google)…

Hmm, this ftrace selftests has been expected to be run without any BPF programs... Is there any other issue on other test cases?

Unfortunately, systemd is starting to add BPF programs :-p

I noticed that my laptop has users.

-- Steve