[PATCH v3 3/3] selftests/mm/charge_reserved_hugetlb.sh: add waits with timeout helper

Li Wang
2025-12-21T12:27:09Z

The hugetlb cgroup usage wait loops in charge_reserved_hugetlb.sh were
unbounded and could hang forever if the expected cgroup file value never
appears (e.g. due to write_to_hugetlbfs in Error mapping).

--- Error log ---
# uname -r
6.12.0-xxx.el10.aarch64+64k

# ls /sys/kernel/mm/hugepages/hugepages-*
hugepages-16777216kB/ hugepages-2048kB/ hugepages-524288kB/

#./charge_reserved_hugetlb.sh -cgroup-v2
# -----------------------------------------
...
# nr hugepages = 10
# writing cgroup limit: 5368709120
# writing reseravation limit: 5368709120
...
# write_to_hugetlbfs: Error mapping the file: Cannot allocate memory
# Waiting for hugetlb memory reservation to reach size 2684354560.
# 0
# Waiting for hugetlb memory reservation to reach size 2684354560.
# 0
# Waiting for hugetlb memory reservation to reach size 2684354560.
# 0
# Waiting for hugetlb memory reservation to reach size 2684354560.
# 0
# Waiting for hugetlb memory reservation to reach size 2684354560.
# 0
# Waiting for hugetlb memory reservation to reach size 2684354560.
# 0
...

Introduce a small helper, wait_for_file_value(), and use it for:
- waiting for reservation usage to drop to 0,
- waiting for reservation usage to reach a given size,
- waiting for fault usage to reach a given size.

This makes the waits consistent and adds a hard timeout (60 tries with
1s sleep) so the test fails instead of stalling indefinitely.

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Waiman Long <longman@redhat.com>
---
.../selftests/mm/charge_reserved_hugetlb.sh | 51 +++++++++++--------
1 file changed, 30 insertions(+), 21 deletions(-)

diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
index fa6713892d82..447769657634 100755
--- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
+++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
@@ -100,7 +100,7 @@ function setup_cgroup() {
echo writing cgroup limit: "$cgroup_limit"
echo "$cgroup_limit" >$cgroup_path/$name/hugetlb.${MB}MB.$fault_limit_file

- echo writing reseravation limit: "$reservation_limit"
+ echo writing reservation limit: "$reservation_limit"
echo "$reservation_limit" > \
$cgroup_path/$name/hugetlb.${MB}MB.$reservation_limit_file

@@ -112,41 +112,50 @@ function setup_cgroup() {
fi
}

+function wait_for_file_value() {
+ local path="$1"
+ local expect="$2"
+ local max_tries=60
+
+ if [[ ! -r "$path" ]]; then
+ echo "ERROR: cannot read '$path', missing or permission denied"
+ return 1
+ fi
+
+ for ((i=1; i<=max_tries; i++)); do
+ local cur="$(cat "$path")"
+ if [[ "$cur" == "$expect" ]]; then
+ return 0
+ fi
+ echo "Waiting for $path to become '$expect' (current: '$cur') (try $i/$max_tries)"
+ sleep 1
+ done
+
+ echo "ERROR: timeout waiting for $path to become '$expect'"
+ return 1
+}
+
function wait_for_hugetlb_memory_to_get_depleted() {
local cgroup="$1"
local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
- # Wait for hugetlbfs memory to get depleted.
- while [ $(cat $path) != 0 ]; do
- echo Waiting for hugetlb memory to get depleted.
- cat $path
- sleep 0.5
- done
+
+ wait_for_file_value "$path" "0"
}

function wait_for_hugetlb_memory_to_get_reserved() {
local cgroup="$1"
local size="$2"
-
local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$reservation_usage_file"
- # Wait for hugetlbfs memory to get written.
- while [ $(cat $path) != $size ]; do
- echo Waiting for hugetlb memory reservation to reach size $size.
- cat $path
- sleep 0.5
- done
+
+ wait_for_file_value "$path" "$size"
}

function wait_for_hugetlb_memory_to_get_written() {
local cgroup="$1"
local size="$2"
-
local path="$cgroup_path/$cgroup/hugetlb.${MB}MB.$fault_usage_file"
- # Wait for hugetlbfs memory to get written.
- while [ $(cat $path) != $size ]; do
- echo Waiting for hugetlb memory to reach size $size.
- cat $path
- sleep 0.5
- done
+
+ wait_for_file_value "$path" "$size"
}

function write_hugetlbfs_and_get_usage() {
--
2.49.0