[LTP] [PATCH] memcg_stress: survive OOM by targeting the stressors

[Andrea Cervesato]

From: Andrea Cervesato <andrea.cervesato@suse.com>

The single-cgroup subtest intentionally lets one process fault in the
whole memory budget to push the system to its memory ceiling, so hitting
the OOM killer is an expected part of the stress. The problem is that the
OOM killer could reap the driver script, turning that expected pressure
into a spurious TBROK.

Mark the stress processes as the preferred OOM victims. A killed stressor
is already reaped and cleaned up by the test, while the driver survives
and reports the result.

Fixes: 02961a7b2bb4 ("memcg_stress_test.sh: Fix reserved mem calculate")
Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
On some systems this might happens:

[  244.207623][T117130] kirk[3061]: memcg_stress: start (command: memcg_stress_test.sh)
[  244.391438][T117164] memcg_stress_te (117164): drop_caches: 3
[ 1444.509722][T119900] kirk[3061]: memcg_stress: end (returncode: -1)
[ 1444.629434][T119934] kirk[3061]: memcg_control: start (command: memcg_control_test.sh)
[ 1445.856012][T120020] mem_process invoked oom-killer: gfp_mask=0xcc0(GFP_KERNEL), order=0, oom_score_adj=0
---
 testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh b/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh
index 47cac9af8bec970b7fb338c5469ab73d55267740..14a5ddeeaa45a1bc5e30b2fa7640bcb1effbd94b 100755
--- a/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh
+++ b/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh
@@ -71,8 +71,12 @@ run_stress()
 	for i in $(seq 0 $(($cgroups-1))); do
 		ROD mkdir "$test_path/$i"
 		memcg_process_stress $mem_size $interval &
-		ROD echo $! \> "$test_path/$i/$task_list"
-		pids="$pids $!"
+		pid=$!
+		ROD echo $pid \> "$test_path/$i/$task_list"
+		# Make the stress process the preferred OOM victim so that memory
+		# pressure kills a stressor rather than the driver script.
+		echo 1000 > "/proc/$pid/oom_score_adj" 2>/dev/null
+		pids="$pids $pid"
 	done
 
 	for pid in $pids; do

---
base-commit: 4898cb95b01b8a3ab5e1ea752990deca7a66ca34
change-id: 20260703-fix_memcg_stress-0c6669bfa5f6

Best regards,
-- 
Andrea Cervesato <andrea.cervesato@suse.com>