[PATCH] selftests/damon/sysfs.py: stop obsolete_target shells hanging the test

[Jaeyeon Lee <jaeyeon.lee.dev@gmail.com>]

The obsolete_target test spawns three 'sh' processes as monitoring
targets.  The processes inherit stdin from the test.  When the test is
run via 'make run_tests' from an interactive terminal, the kselftest
runner executes it under 'timeout', which puts it in a background
process group.  The 'sh' processes then try to read the terminal, so
the kernel sends SIGTTIN to the whole process group.  This stops the
'sh' processes, and also the child the test has just forked to spawn
the next 'sh', before it can run 'sh'.  The test then waits on that
child forever, until the kselftest runner kills it after 45 seconds.
The test passes when run directly.

Fix this by passing stdin=subprocess.PIPE when spawning the processes.
The processes then read from a pipe that never receives input, so they
stay alive and idle as the test expects.

Assisted-by: LLM
Signed-off-by: Jaeyeon Lee <jaeyeon.lee.dev@gmail.com>
---
 tools/testing/selftests/damon/sysfs.py | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/damon/sysfs.py b/tools/testing/selftests/damon/sysfs.py
index 66c826189320..ce54fa21c09f 100755
--- a/tools/testing/selftests/damon/sysfs.py
+++ b/tools/testing/selftests/damon/sysfs.py
@@ -390,12 +390,12 @@ def main():
     kdamonds.stop()
 
     # test obsolete_target.
-    proc1 = subprocess.Popen(['sh'], stdout=subprocess.PIPE,
-                             stderr=subprocess.PIPE)
-    proc2 = subprocess.Popen(['sh'], stdout=subprocess.PIPE,
-                             stderr=subprocess.PIPE)
-    proc3 = subprocess.Popen(['sh'], stdout=subprocess.PIPE,
-                             stderr=subprocess.PIPE)
+    proc1 = subprocess.Popen(['sh'], stdin=subprocess.PIPE,
+                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    proc2 = subprocess.Popen(['sh'], stdin=subprocess.PIPE,
+                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    proc3 = subprocess.Popen(['sh'], stdin=subprocess.PIPE,
+                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     kdamonds = _damon_sysfs.Kdamonds(
             [_damon_sysfs.Kdamond(
                 contexts=[_damon_sysfs.DamonCtx(
-- 
2.43.0