linux-kernel - [PATCH] selftests/ftrace: Fix event filter target

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Date: Wed, 20 Mar 2024 14:18:44 +0000
From: Mark Rutland <mark.rutland@....com>
To: linux-kernel@...r.kernel.org
Cc: aishwarya.tcv@....com,
	linux-kselftest@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	mark.rutland@....com,
	mathieu.desnoyers@...icios.com,
	mhiramat@...nel.org,
	rostedt@...dmis.org,
	shuah@...nel.org
Subject: [PATCH] selftests/ftrace: Fix event filter target_func selection

The event filter function test has been failing in our internal test
farm:

| # not ok 33 event filter function - test event filtering on functions

Running the test in verbose mode indicates that this is because the test
erroneously determines that kmem_cache_free() is the most common caller
of kmem_cache_free():

  # # + cut -d: -f3 trace
  # # + sed s/call_site=([^+]*)+0x.*/1/
  # # + sort
  # # + uniq -c
  # # + sort
  # # + tail -n 1
  # # + sed s/^[ 0-9]*//
  # # + target_func=kmem_cache_free

.. and as kmem_cache_free() doesn't call itself, setting this as the
filter function for kmem_cache_free() results in no hits, and
consequently the test fails:

  # # + grep kmem_cache_free trace
  # # + grep kmem_cache_free
  # # + wc -l
  # # + hitcnt=0
  # # + grep kmem_cache_free trace
  # # + grep -v kmem_cache_free
  # # + wc -l
  # # + misscnt=0
  # # + [ 0 -eq 0 ]
  # # + exit_fail

This seems to be because the system in question has tasks with ':' in
their name (which a number of kernel worker threads have). These show up
in the trace, e.g.

  test:.sh-1299    [004] .....  2886.040608: kmem_cache_free: call_site=putname+0xa4/0xc8 ptr=000000000f4d22f4 name=names_cache

.. and so when we try to extact the call_site with:

  cut -d: -f3 trace | sed 's/call_site=\([^+]*\)+0x.*/\1/'

.. the 'cut' command will extrace the column containing
'kmem_cache_free' rather than the column containing 'call_site=...', and
the 'sed' command will leave this unchanged. Consequently, the test will
decide to use 'kmem_cache_free' as the filter function, resulting in the
failure seen above.

Fix this by matching the 'call_site=<func>' part specifically to extract
the function name.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Reported-by: Aishwarya TCV <aishwarya.tcv@....com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org
Cc: linux-kselftest@...r.kernel.org
Cc: linux-trace-kernel@...r.kernel.org
---
 .../selftests/ftrace/test.d/filter/event-filter-function.tc     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc b/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc
index 2de7c61d1ae3..3f74c09c56b6 100644
--- a/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc
+++ b/tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc
@@ -24,7 +24,7 @@ echo 0 > events/enable
 echo "Get the most frequently calling function"
 sample_events
 
-target_func=`cut -d: -f3 trace | sed 's/call_site=\([^+]*\)+0x.*/\1/' | sort | uniq -c | sort | tail -n 1 | sed 's/^[ 0-9]*//'`
+target_func=`cat trace | grep -o 'call_site=\([^+]*\)' | sed 's/call_site=//' | sort | uniq -c | sort | tail -n 1 | sed 's/^[ 0-9]*//'`
 if [ -z "$target_func" ]; then
     exit_fail
 fi
-- 
2.39.2