On Mon, Dec 22, 2025 at 4:30 AM Waiman Long llong@redhat.com wrote:
On 12/21/25 7:26 AM, Li Wang wrote:
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" "$size" }
function write_hugetlbfs_and_get_usage() {
wait_for_file_value() now return 0 onr success and 1 on timeout. However, none of the callers of the wait_for_hugetlb_memory* are checking their return values and acting accordingly. Are we expecting that the test will show failure because the waiting isn't completed or should we explicitly exit with ksft_fail (1) value?
Hmm, it seems the test shouldn't exit too early.
As the wait_for_hugetlb_memory* is only trying 60s to examine the file value, if timeouted, we still need to keep going because the test requires CLEANUP work and exit/report from there.
The key point of each subtest is to save the '$write_result' value and examine it which controls the whole test to exit.
e.g.
This is an intentional error test:
# ./charge_reserved_hugetlb.sh -cgroup-v2 CLEANUP DONE ... Writing to this path: /mnt/huge/test Writing this size: 2684354560 Not populating. Not writing to memory. Using method=0 Shared mapping. RESERVE mapping. Allocating using HUGETLBFS. write_to_hugetlbfs: Error mapping the file: Cannot allocate memory Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current to become '2684354560' (current: '0') (try 1/60) Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current to become '2684354560' (current: '0') (try 2/60) Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current to become '2684354560' (current: '0') (try 3/60) Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current to become '2684354560' (current: '0') (try 4/60) ... Waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current to become '2684354560' (current: '0') (try 60/60) ERROR: timeout waiting for /sys/fs/cgroup/hugetlb_cgroup_test/hugetlb.512MB.rsvd.current to become '2684354560' After write: hugetlb_usage=0 reserved_usage=0 0 0 Memory charged to hugtlb=0 Memory charged to reservation=0 expected (2684354560) != actual (0): Reserved memory not charged to reservation usage. CLEANUP DONE