Add test_hk_noise_isolated() to test_cpuset_prs.sh to verify that
creating and destroying an isolated partition updates the kernel-noise
housekeeping state, including the /sys/devices/system/cpu/nohz_full
attribute.  Add the cpu_in_cpulist() helper to correctly test membership
against a cpulist that may contain ranges.

Also detect and report whether the test is running in zero-boot-param
mode (no nohz_full= in /proc/cmdline).  When in zero-boot-param mode
the test confirms that nohz_full is activated by the DHM runtime path,
verifying that dhm_cycle_isolated_cpus() correctly enables tick
isolation without any boot-time setup.

Co-developed-by: Qiliang Yuan <[email protected]>
Signed-off-by: Qiliang Yuan <[email protected]>
Signed-off-by: Jing Wu <[email protected]>
---
 tools/testing/selftests/cgroup/test_cpuset_prs.sh | 580 +++++++++++++++++++++-
 1 file changed, 579 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh 
b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index a56f4153c64df..ce16734545505 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -20,7 +20,7 @@ skip_test() {
 WAIT_INOTIFY=$(cd $(dirname $0); pwd)/wait_inotify
 
 # Find cgroup v2 mount point
-CGROUP2=$(mount -t cgroup2 | head -1 | awk -e '{print $3}')
+CGROUP2=$(mount -t cgroup2 | head -1 | awk '{print $3}')
 [[ -n "$CGROUP2" ]] || skip_test "Cgroup v2 mount point not found!"
 SUBPARTS_CPUS=$CGROUP2/.__DEBUG__.cpuset.cpus.subpartitions
 CPULIST=$(cat $CGROUP2/cpuset.cpus.effective)
@@ -1204,9 +1204,587 @@ test_inotify()
        echo "" > cpuset.cpus
 }
 
+#
+# cpu_in_cpulist <cpu> <cpulist>
+#
+# Return 0 if <cpu> appears in <cpulist> (a kernel cpumask list such as
+# "0-3,8-31"), non-zero otherwise.  The kernel cpulist format uses ranges
+# ("lo-hi") and comma-separated items; a simple grep cannot detect that a
+# number falls in the middle of a range, so walk each element explicitly.
+#
+cpu_in_cpulist()
+{
+       local cpu=$1 list=$2 range lo hi
+       for range in $(echo "$list" | tr ',' ' '); do
+               if [[ "$range" == *-* ]]; then
+                       lo=${range%-*}
+                       hi=${range#*-}
+                       [[ $cpu -ge $lo && $cpu -le $hi ]] && return 0
+               else
+                       [[ $cpu -eq $range ]] && return 0
+               fi
+       done
+       return 1
+}
+
+#
+# verify_nohz_exact <baseline> <active_cpus> <current>
+#
+# Verify that <current> nohz_full equals <baseline> ∪ <active_cpus>.
+# <active_cpus> may be a cpulist range ("4-7") or empty string ("").
+# Catches both missing CPUs and unexpected extra CPUs.
+#
+verify_nohz_exact()
+{
+       local baseline=$1 active=$2 current=$3 cpu exp got
+       for cpu in $(seq 0 $((NR_CPUS - 1))); do
+               exp=0; got=0
+               cpu_in_cpulist $cpu "$baseline" && exp=1
+               [[ -n "$active" ]] && cpu_in_cpulist $cpu "$active" && exp=1
+               cpu_in_cpulist $cpu "$current" && got=1
+               [[ $exp -eq $got ]] || {
+                       if [[ $got -eq 0 ]]; then
+                               echo "FAIL: cpu${cpu} expected in nohz_full but 
absent" \
+                                    "(baseline='$baseline' active='$active'" \
+                                    "current='$current')"
+                       else
+                               echo "FAIL: cpu${cpu} unexpectedly in 
nohz_full" \
+                                    "(baseline='$baseline' active='$active'" \
+                                    "current='$current')"
+                       fi
+                       return 1
+               }
+       done
+       return 0
+}
+
+#
+# Test that isolated partition creation/destruction drives kernel-noise
+# housekeeping mask updates and remains correct under pressure.
+#
+# Requires: >=8 CPUs, no isolcpus= boot conflict, root
+#
+
+#
+# hk_noise_check_nocb_affinity <cpulist> <expect_isolated>
+#
+# When expect_isolated=1: verify rcuop/N kthreads for CPUs in cpulist do NOT
+# include those CPUs in their scheduler affinity (RCU NOCB active — callbacks
+# for the isolated CPU are offloaded to a different CPU).
+# When expect_isolated=0: verify CPUs are back in affinity (NOCB restored).
+# Silently skips CPUs whose rcuop/N thread is absent (no NOCB support).
+#
+hk_noise_check_nocb_affinity()
+{
+       local cpulist=$1 expect_isolated=$2
+       local cpu lo hi range pid aff_hex rev_hex nibble_pos nibble_char
+       local nibble_val bit_in_nibble bit failed=0
+
+       command -v taskset > /dev/null 2>&1 || return 0
+
+       for range in $(echo "$cpulist" | tr ',' ' '); do
+               if [[ "$range" == *-* ]]; then
+                       lo=${range%-*}; hi=${range#*-}
+               else
+                       lo=$range; hi=$range
+               fi
+               for cpu in $(seq "$lo" "$hi"); do
+                       pid=$(ps -eo pid,comm | awk -v c="rcuop/$cpu" 
'$2==c{print $1}')
+                       [[ -n "$pid" ]] || continue
+                       aff_hex=$(taskset -p "$pid" 2>/dev/null | awk '{print 
$NF}')
+                       [[ -n "$aff_hex" ]] || continue
+
+                       # Extract bit <cpu> from the hex affinity mask.
+                       # Each hex digit covers 4 CPUs; reverse the string to
+                       # work from the LSB side.
+                       rev_hex=$(echo "$aff_hex" | rev)
+                       nibble_pos=$((cpu / 4))
+                       nibble_char=${rev_hex:$nibble_pos:1}
+                       if [[ -z "$nibble_char" ]]; then
+                               nibble_val=0
+                       else
+                               nibble_val=$((16#$nibble_char))
+                       fi
+                       bit_in_nibble=$((cpu % 4))
+                       bit=$(( (nibble_val >> bit_in_nibble) & 1 ))
+
+                       if [[ $expect_isolated -eq 1 && $bit -eq 1 ]]; then
+                               echo "FAIL: rcuop/$cpu affinity still includes" 
\
+                                    "CPU$cpu after isolation (mask=0x$aff_hex)"
+                               failed=1
+                       elif [[ $expect_isolated -eq 0 && $bit -eq 0 ]]; then
+                               echo "FAIL: rcuop/$cpu affinity still excludes" 
\
+                                    "CPU$cpu after de-isolation 
(mask=0x$aff_hex)"
+                               failed=1
+                       fi
+               done
+       done
+       return $failed
+}
+
+test_hk_noise_isolated()
+{
+       local ISOL_BEFORE TEST_CPUS i PART ISOL_AFTER ISOL_RESTORE
+       local NOHZ_FILE NOHZ_BEFORE NOHZ_AFTER NOHZ_RESTORE
+       local HK_NOHZ_CHECK=0
+       local LOOPS=100
+       local CMDLINE HAS_BOOT_NOHZ=0
+       local DMESG_LINES_START
+       DMESG_LINES_START=$(dmesg | wc -l)
+
+       [[ $NR_CPUS -ge 8 ]] || {
+               echo "HK-noise test skipped: need >=8 CPUs, have $NR_CPUS"
+               return 0
+       }
+
+       # Detect whether CONFIG_NO_HZ_FULL is active: the sysfs attribute
+       # /sys/devices/system/cpu/nohz_full exposes the current nohz_full
+       # cpumask and is only present when NO_HZ_FULL is enabled.
+       NOHZ_FILE=/sys/devices/system/cpu/nohz_full
+       [[ -r "$NOHZ_FILE" ]] && HK_NOHZ_CHECK=1
+
+       # Determine if running in zero-boot-param mode.  DHM activates tick
+       # and RCU-NOCB isolation at runtime; no nohz_full= or rcu_nocbs=
+       # kernel boot parameters are required.
+       { read -r CMDLINE < /proc/cmdline; } 2>/dev/null || CMDLINE=""
+       [[ $CMDLINE = *nohz_full=* ]] && HAS_BOOT_NOHZ=1
+       if [[ $HAS_BOOT_NOHZ -eq 0 ]]; then
+               console_msg "HK-noise: zero-boot-param mode" \
+                           "(no nohz_full= in /proc/cmdline -- testing DHM 
runtime path)"
+       else
+               console_msg "HK-noise: boot-param mode (nohz_full= present at 
boot)"
+       fi
+
+       cd $CGROUP2/test
+       echo member > cpuset.cpus.partition 2>/dev/null
+       echo "" > cpuset.cpus 2>/dev/null
+
+       ISOL_BEFORE=$(cat $CGROUP2/cpuset.cpus.isolated)
+       [[ $HK_NOHZ_CHECK -eq 1 ]] && NOHZ_BEFORE=$(cat $NOHZ_FILE)
+       TEST_CPUS="4-7"
+       echo $TEST_CPUS > cpuset.cpus
+
+       #
+       # Basic create/destroy cycle — verify domain isolation and
+       # kernel-noise (nohz_full) changes together.
+       #
+       console_msg "HK-noise: basic create/destroy cycle"
+       echo isolated > cpuset.cpus.partition
+
+       ISOL_AFTER=$(cat $CGROUP2/cpuset.cpus.isolated)
+       [[ $ISOL_AFTER != "$ISOL_BEFORE" ]] || {
+               echo "FAIL: isolated set unchanged after partition create"
+               exit 1
+       }
+
+       if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+               NOHZ_AFTER=$(cat $NOHZ_FILE)
+               verify_nohz_exact "$NOHZ_BEFORE" "$TEST_CPUS" "$NOHZ_AFTER" || 
exit 1
+               console_msg "HK-noise: nohz_full after isolation: $NOHZ_AFTER"
+       fi
+
+       # Verify RCU NOCB: rcuop/N kthreads for isolated CPUs must have those
+       # CPUs removed from their scheduler affinity mask.
+       hk_noise_check_nocb_affinity "$TEST_CPUS" 1 || exit 1
+
+       echo member > cpuset.cpus.partition
+
+       ISOL_RESTORE=$(cat $CGROUP2/cpuset.cpus.isolated)
+       [[ $ISOL_RESTORE = "$ISOL_BEFORE" ]] || {
+               echo "FAIL: expected '$ISOL_BEFORE' after destroy, got 
'$ISOL_RESTORE'"
+               exit 1
+       }
+
+       if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+               NOHZ_RESTORE=$(cat $NOHZ_FILE)
+               verify_nohz_exact "$NOHZ_BEFORE" "" "$NOHZ_RESTORE" || exit 1
+       fi
+
+       # Verify RCU NOCB restored: isolated CPUs must reappear in rcuop/N 
affinity.
+       hk_noise_check_nocb_affinity "$TEST_CPUS" 0 || exit 1
+
+       #
+       # Reject all-CPU isolation (must leave at least one housekeeping CPU)
+       #
+       console_msg "HK-noise: reject all-CPU isolation"
+       echo 0-$((NR_CPUS - 1)) > cpuset.cpus
+       echo isolated > cpuset.cpus.partition
+       PART=$(cat cpuset.cpus.partition)
+       [[ $PART = *invalid* || $PART = member ]] || {
+               echo "FAIL: all-CPU isolation was not rejected, got '$PART'"
+               exit 1
+       }
+
+       #
+       # SMT safety: partial sibling isolation
+       #
+       console_msg "HK-noise: SMT sibling constraint"
+       echo $TEST_CPUS > cpuset.cpus
+       echo isolated > cpuset.cpus.partition
+       PART=$(cat cpuset.cpus.partition)
+       [[ $PART = isolated ]] || {
+               echo "FAIL: could not create isolated partition, got '$PART'"
+               exit 1
+       }
+       echo member > cpuset.cpus.partition
+
+       #
+       # Non-hotpluggable CPU: must be skipped with a kernel warning without
+       # rejecting the partition; hotpluggable peers must still be isolated.
+       #
+       # A CPU whose online file is absent (e.g. CPU 0 on x86-64) has hotplug
+       # disabled.  DHM emits pr_warn_once and keeps it in the tick/RCU-NOCB
+       # housekeeping set; it must not appear in nohz_full after isolation.
+       # The remaining hotpluggable CPUs in the partition must still be 
isolated.
+       #
+       local FIXED_CPU="" c NOHZ_NOW
+       for c in $(seq 0 $((NR_CPUS - 1))); do
+               [[ -f /sys/devices/system/cpu/cpu${c}/online ]] || {
+                       FIXED_CPU=$c
+                       break
+               }
+       done
+       if [[ -n "$FIXED_CPU" ]]; then
+               console_msg "HK-noise: non-hotpluggable CPU${FIXED_CPU} skip"
+               echo "${FIXED_CPU},${TEST_CPUS}" > cpuset.cpus
+               echo isolated > cpuset.cpus.partition
+               PART=$(cat cpuset.cpus.partition)
+               [[ $PART = isolated ]] || {
+                       echo "FAIL: partition rejected when including 
non-hotpluggable" \
+                            "CPU${FIXED_CPU}: got '$PART'"
+                       exit 1
+               }
+               if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+                       NOHZ_NOW=$(cat $NOHZ_FILE)
+                       if cpu_in_cpulist $FIXED_CPU "$NOHZ_NOW"; then
+                               echo "FAIL: non-hotpluggable CPU${FIXED_CPU} 
appeared" \
+                                    "in nohz_full (should be skipped)"
+                               exit 1
+                       fi
+                       local lo hi
+                       lo=${TEST_CPUS%%-*}
+                       hi=${TEST_CPUS##*-}
+                       for cpu in $(seq "$lo" "$hi"); do
+                               if ! cpu_in_cpulist $cpu "$NOHZ_NOW"; then
+                                       echo "FAIL: hotpluggable cpu${cpu} 
missing from" \
+                                            "nohz_full in mixed partition 
(got: '$NOHZ_NOW')"
+                                       exit 1
+                               fi
+                       done
+                       console_msg "HK-noise: CPU${FIXED_CPU} absent, 
${TEST_CPUS} present" \
+                                   "in nohz_full: $NOHZ_NOW"
+               fi
+               echo member > cpuset.cpus.partition
+               echo $TEST_CPUS > cpuset.cpus
+       else
+               console_msg "HK-noise: all CPUs hotpluggable; skip 
non-hotpluggable subtest"
+       fi
+
+       #
+       # Delta isolation: modify cpuset.cpus while the partition is isolated.
+       # dhm_prev_isolated must track the delta and update nohz_full in step.
+       #
+       local lo hi mid lower_cpus upper_cpu
+       lo=${TEST_CPUS%%-*}
+       hi=${TEST_CPUS##*-}
+       mid=$(( lo + (hi - lo) / 2 ))
+       lower_cpus="${lo}-${mid}"
+       upper_cpu=$(( mid + 1 ))
+       console_msg "HK-noise: delta isolation (shrink ${TEST_CPUS} → 
${lower_cpus})"
+       echo $TEST_CPUS > cpuset.cpus
+       echo isolated > cpuset.cpus.partition
+       PART=$(cat cpuset.cpus.partition)
+       [[ $PART = isolated ]] || {
+               echo "FAIL: delta test: initial isolation failed, got '$PART'"
+               exit 1
+       }
+       echo $lower_cpus > cpuset.cpus
+       PART=$(cat cpuset.cpus.partition)
+       if [[ $PART = isolated ]]; then
+               if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+                       NOHZ_NOW=$(cat $NOHZ_FILE)
+                       verify_nohz_exact "$NOHZ_BEFORE" "$lower_cpus" 
"$NOHZ_NOW" || exit 1
+               fi
+               # Expand back to full TEST_CPUS and re-verify
+               echo $TEST_CPUS > cpuset.cpus
+               if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+                       NOHZ_NOW=$(cat $NOHZ_FILE)
+                       verify_nohz_exact "$NOHZ_BEFORE" "$TEST_CPUS" 
"$NOHZ_NOW" || exit 1
+               fi
+               echo member > cpuset.cpus.partition
+               if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+                       NOHZ_NOW=$(cat $NOHZ_FILE)
+                       verify_nohz_exact "$NOHZ_BEFORE" "" "$NOHZ_NOW" || exit 
1
+               fi
+       else
+               console_msg "HK-noise: delta test: partition invalidated on 
shrink" \
+                           "('$PART') -- cpuset constraint, not a DHM bug; 
skipping"
+               echo member > cpuset.cpus.partition 2>/dev/null || true
+       fi
+       echo $TEST_CPUS > cpuset.cpus
+
+       #
+       # Nested partition: parent root → child isolated
+       #
+       console_msg "HK-noise: nested partition inheritance"
+       echo $TEST_CPUS > cpuset.cpus
+       test_partition root
+       mkdir -p HK_SUB
+       cd HK_SUB
+       echo "${lo}-$((lo + 1))" > cpuset.cpus
+       echo isolated > cpuset.cpus.partition
+       ISOL_AFTER=$(cat $CGROUP2/cpuset.cpus.isolated)
+       [[ -n $ISOL_AFTER ]] || {
+               echo "FAIL: nested isolated partition not reflected in 
cpuset.cpus.isolated"
+               exit 1
+       }
+       echo member > cpuset.cpus.partition
+       cd $CGROUP2/test
+       echo member > cpuset.cpus.partition
+       rmdir HK_SUB 2>/dev/null
+
+       #
+       # Pressure test: 100 create/destroy cycles with nohz_full verified
+       # on every cycle to catch mid-run state corruption.
+       #
+       console_msg "HK-noise: pressure test ($LOOPS cycles)"
+       echo $TEST_CPUS > cpuset.cpus
+       for i in $(seq 1 $LOOPS); do
+               echo isolated > cpuset.cpus.partition
+               PART=$(cat cpuset.cpus.partition)
+               [[ $PART = isolated ]] || {
+                       echo "FAIL: cycle $i create failed, got '$PART'"
+                       exit 1
+               }
+               if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+                       NOHZ_NOW=$(cat $NOHZ_FILE)
+                       verify_nohz_exact "$NOHZ_BEFORE" "$TEST_CPUS" 
"$NOHZ_NOW" || {
+                               echo "FAIL: nohz_full wrong at cycle $i 
(isolated)"
+                               exit 1
+                       }
+               fi
+               echo member > cpuset.cpus.partition
+               PART=$(cat cpuset.cpus.partition)
+               [[ $PART = member ]] || {
+                       echo "FAIL: cycle $i destroy failed, got '$PART'"
+                       exit 1
+               }
+               if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+                       NOHZ_NOW=$(cat $NOHZ_FILE)
+                       verify_nohz_exact "$NOHZ_BEFORE" "" "$NOHZ_NOW" || {
+                               echo "FAIL: nohz_full wrong at cycle $i 
(member)"
+                               exit 1
+                       }
+               fi
+       done
+
+       #
+       # Stability: after pressure test, verify final state
+       #
+       console_msg "HK-noise: post-pressure cleanup"
+       echo isolated > cpuset.cpus.partition
+       ISOL_AFTER=$(cat $CGROUP2/cpuset.cpus.isolated)
+       [[ -n $ISOL_AFTER ]] || {
+               echo "FAIL: isolated set empty after pressure test"
+               exit 1
+       }
+       echo member > cpuset.cpus.partition
+       echo "" > cpuset.cpus
+       ISOL_RESTORE=$(cat $CGROUP2/cpuset.cpus.isolated)
+       [[ $ISOL_RESTORE = "$ISOL_BEFORE" ]] || {
+               echo "FAIL: final isolated '$ISOL_RESTORE' != '$ISOL_BEFORE'"
+               exit 1
+       }
+
+       if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+               NOHZ_RESTORE=$(cat $NOHZ_FILE)
+               [[ "$NOHZ_RESTORE" = "$NOHZ_BEFORE" ]] || {
+                       echo "FAIL: nohz_full not restored after pressure 
test:" \
+                            "expected '$NOHZ_BEFORE', got '$NOHZ_RESTORE'"
+                       exit 1
+               }
+       fi
+
+       #
+       # Pressure with resident task: create/destroy cycles while a sleeping
+       # task occupies the isolated partition.  Exercises the dhm_cycling_cpus
+       # suppression path that prevents false partition invalidation when a
+       # task is present during hotplug cycling steps.
+       #
+       console_msg "HK-noise: pressure with resident task ($LOOPS cycles)"
+       echo $TEST_CPUS > cpuset.cpus
+       sleep 600 &
+       local TASK_PID=$!
+       echo $TASK_PID > cgroup.procs
+       for i in $(seq 1 $LOOPS); do
+               echo isolated > cpuset.cpus.partition
+               PART=$(cat cpuset.cpus.partition)
+               [[ $PART = isolated ]] || {
+                       echo "FAIL: task-occupied cycle $i create failed, got 
'$PART'"
+                       kill $TASK_PID 2>/dev/null; wait $TASK_PID 2>/dev/null
+                       exit 1
+               }
+               if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+                       NOHZ_NOW=$(cat $NOHZ_FILE)
+                       verify_nohz_exact "$NOHZ_BEFORE" "$TEST_CPUS" 
"$NOHZ_NOW" || {
+                               kill $TASK_PID 2>/dev/null; wait $TASK_PID 
2>/dev/null
+                               exit 1
+                       }
+               fi
+               echo member > cpuset.cpus.partition
+               PART=$(cat cpuset.cpus.partition)
+               [[ $PART = member ]] || {
+                       echo "FAIL: task-occupied cycle $i destroy failed, got 
'$PART'"
+                       kill $TASK_PID 2>/dev/null; wait $TASK_PID 2>/dev/null
+                       exit 1
+               }
+       done
+       kill $TASK_PID 2>/dev/null
+       wait $TASK_PID 2>/dev/null
+       echo "" > cpuset.cpus
+
+       #
+       # Concurrent partitions: two sibling cgroups each holding half of
+       # TEST_CPUS simultaneously isolated.  Verifies independent isolation
+       # and correct union in cpuset.cpus.isolated / nohz_full.
+       #
+       local lo hi mid lower_half upper_half NOHZ_BOTH
+       lo=${TEST_CPUS%%-*}; hi=${TEST_CPUS##*-}
+       mid=$(( lo + (hi - lo) / 2 ))
+       lower_half="${lo}-${mid}"
+       upper_half="$((mid + 1))-${hi}"
+       console_msg "HK-noise: concurrent partitions ($lower_half and 
$upper_half)"
+       echo $TEST_CPUS > cpuset.cpus
+       echo root > cpuset.cpus.partition
+       mkdir -p HK_A HK_B
+       echo "$lower_half" > HK_A/cpuset.cpus
+       echo isolated > HK_A/cpuset.cpus.partition
+       echo "$upper_half" > HK_B/cpuset.cpus
+       echo isolated > HK_B/cpuset.cpus.partition
+       local PA PB
+       PA=$(cat HK_A/cpuset.cpus.partition)
+       PB=$(cat HK_B/cpuset.cpus.partition)
+       [[ $PA = isolated ]] || {
+               echo "FAIL: concurrent partition HK_A not isolated, got '$PA'"
+               echo member > HK_A/cpuset.cpus.partition 2>/dev/null
+               echo member > HK_B/cpuset.cpus.partition 2>/dev/null
+               rmdir HK_A HK_B 2>/dev/null
+               echo member > cpuset.cpus.partition 2>/dev/null
+               exit 1
+       }
+       [[ $PB = isolated ]] || {
+               echo "FAIL: concurrent partition HK_B not isolated, got '$PB'"
+               echo member > HK_A/cpuset.cpus.partition 2>/dev/null
+               echo member > HK_B/cpuset.cpus.partition 2>/dev/null
+               rmdir HK_A HK_B 2>/dev/null
+               echo member > cpuset.cpus.partition 2>/dev/null
+               exit 1
+       }
+       if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+               NOHZ_BOTH=$(cat $NOHZ_FILE)
+               verify_nohz_exact "$NOHZ_BEFORE" "$TEST_CPUS" "$NOHZ_BOTH" || {
+                       echo member > HK_A/cpuset.cpus.partition 2>/dev/null
+                       echo member > HK_B/cpuset.cpus.partition 2>/dev/null
+                       rmdir HK_A HK_B 2>/dev/null
+                       echo member > cpuset.cpus.partition 2>/dev/null
+                       exit 1
+               }
+       fi
+       hk_noise_check_nocb_affinity "$TEST_CPUS" 1 || {
+               echo member > HK_A/cpuset.cpus.partition 2>/dev/null
+               echo member > HK_B/cpuset.cpus.partition 2>/dev/null
+               rmdir HK_A HK_B 2>/dev/null
+               echo member > cpuset.cpus.partition 2>/dev/null
+               exit 1
+       }
+       echo member > HK_A/cpuset.cpus.partition
+       echo member > HK_B/cpuset.cpus.partition
+       rmdir HK_A HK_B
+       echo member > cpuset.cpus.partition
+       if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+               NOHZ_NOW=$(cat $NOHZ_FILE)
+               verify_nohz_exact "$NOHZ_BEFORE" "" "$NOHZ_NOW" || exit 1
+       fi
+       hk_noise_check_nocb_affinity "$TEST_CPUS" 0 || exit 1
+       echo "" > cpuset.cpus
+
+       #
+       # Concurrent create/destroy: two background subshells race on the same
+       # partition simultaneously.  Verifies that concurrent cpuset writes
+       # do not corrupt kernel state or trigger warnings.
+       #
+       console_msg "HK-noise: concurrent create/destroy race"
+       echo $TEST_CPUS > cpuset.cpus
+       local RACE_LOOPS=30 RACE_PID1 RACE_PID2
+       (for i in $(seq 1 $RACE_LOOPS); do
+               echo isolated > cpuset.cpus.partition 2>/dev/null
+               echo member   > cpuset.cpus.partition 2>/dev/null
+       done) &
+       RACE_PID1=$!
+       (for i in $(seq 1 $RACE_LOOPS); do
+               echo member   > cpuset.cpus.partition 2>/dev/null
+               echo isolated > cpuset.cpus.partition 2>/dev/null
+       done) &
+       RACE_PID2=$!
+       wait $RACE_PID1 $RACE_PID2
+       # Drive to a known-good state regardless of who won the last write.
+       echo member > cpuset.cpus.partition 2>/dev/null || true
+       PART=$(cat cpuset.cpus.partition)
+       [[ $PART = member ]] || {
+               echo "FAIL: concurrent race left partition in bad state: 
'$PART'"
+               exit 1
+       }
+       if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+               NOHZ_NOW=$(cat $NOHZ_FILE)
+               verify_nohz_exact "$NOHZ_BEFORE" "" "$NOHZ_NOW" || exit 1
+       fi
+       echo "" > cpuset.cpus
+
+       #
+       # Kernel hard-error check: none of the above scenarios must have
+       # triggered a BUG, OOPS, panic, or RCU stall in the kernel log.
+       # Also catch WARNINGs that implicate our subsystems (cpuset / rcu /
+       # nohz / housekeeping / irq_affinity); ignore unrelated WARNINGs from
+       # other kernel subsystems or user-space processes.
+       #
+       console_msg "HK-noise: checking kernel log for errors"
+       local new_errors
+       new_errors=$(dmesg | tail -n "+$((DMESG_LINES_START + 1))" | \
+               grep -c -E \
+                 'kernel BUG at|OOPS|Kernel panic|RCU Stall|scheduling while 
atomic' \
+               || true)
+       local new_subsys_warns
+       new_subsys_warns=$(dmesg | tail -n "+$((DMESG_LINES_START + 1))" | \
+               grep 'WARNING:' | \
+               grep -c -E 'cpuset|rcu|nohz|housekeeping|irq_affinity|dhm' \
+               || true)
+       local total_errors=$(( new_errors + new_subsys_warns ))
+       [[ $total_errors -eq 0 ]] || {
+               echo "FAIL: $total_errors kernel error(s)/warning(s) during 
HK-noise test:"
+               dmesg | tail -n "+$((DMESG_LINES_START + 1))" | \
+                       grep -E 'kernel BUG at|OOPS|Kernel panic|RCU 
Stall|scheduling while atomic' | head -10
+               dmesg | tail -n "+$((DMESG_LINES_START + 1))" | \
+                       grep 'WARNING:' | grep -E 
'cpuset|rcu|nohz|housekeeping|irq_affinity|dhm' | head -10
+               exit 1
+       }
+
+       cd $CGROUP2
+       if [[ $HK_NOHZ_CHECK -eq 1 ]]; then
+               if [[ $HAS_BOOT_NOHZ -eq 0 ]]; then
+                       console_msg "HK-noise: PASSED" \
+                                   "(zero-boot-param: nohz_full verified via 
DHM runtime path)"
+               else
+                       console_msg "HK-noise: PASSED (with nohz_full 
verification)"
+               fi
+       else
+               console_msg "HK-noise: PASSED (nohz_full skipped: 
CONFIG_NO_HZ_FULL not active)"
+       fi
+}
+
 trap cleanup 0 2 3 6
 run_state_test TEST_MATRIX
 run_remote_state_test REMOTE_TEST_MATRIX
 test_isolated
 test_inotify
+test_hk_noise_isolated
 echo "All tests PASSED."

-- 
2.43.0


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