David Hildenbrand (Red Hat) <[email protected]> wrote: > On 12/21/25 09:58, 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 bugs, timing issues, or unexpected behavior). > > Did you actually hit that in practice? Just wondering.
Yes. On an aarch64 64k setup with 512MB hugepages, the test failed earlier (hugetlbfs got mounted with an effective size of 0 due to size=256M), so write_to_hugetlbfs couldn’t allocate the expected pages. After that, the script’s wait loops never observed the target value, so they spun forever. Detail see below logs. > > > > > --- 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 (120 tries with > > 0.5s sleep) so the test fails instead of stalling indefinitely. > > > > Signed-off-by: Li Wang <[email protected]> > > Cc: David Hildenbrand <[email protected]> > > Cc: Mark Brown <[email protected]> > > Cc: Shuah Khan <[email protected]> > > Cc: Waiman Long <[email protected]> > > --- > > .../selftests/mm/charge_reserved_hugetlb.sh | 47 ++++++++++--------- > > 1 file changed, 26 insertions(+), 21 deletions(-) > > > > diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh > > b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh > > index e1fe16bcbbe8..249a5776c074 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 +112,46 @@ function setup_cgroup() { > > fi > > } > > > > +function wait_for_file_value() { > > + local path="$1" > > + local expect="$2" > > + local max_tries="120" > > + > > + local i cur > > I would just move "cur" into the loop; I don't see a reason to print it > on the error path when you printed the value on the last "Waiting" line? > > local cur="$(cat "$path")" +1 > > Also, not sure if you really need the "local i" here. > > What if the path does not exist, do we want to catch that earlier and > bail out instead of letting "cat" fail here? Yes, we can add a file check before the "cat" loop. > > > + for ((i=1; i<=max_tries; i++)); do > > + cur="$(cat "$path")" > > + if [[ "$cur" == "$expect" ]]; then > > + return 0 > > + fi > > + echo "Waiting for $path to become '$expect' (current: '$cur') (try > > $i/$max_tries)" > > + sleep 0.5 > > Any reason we don't go for the more intuitive "wait 1s" - max 60s wait? Sure, the total loop time are same. -- Regards, Li Wang
