[PATCH v4 01/15] selftests/mm: restore default nr_hugepages value via EXIT trap in charge_reserved_hugetlb.sh

[Sayali Patil <sayalip@linux.ibm.com>]

cleanup() resets nr_hugepages to 0 on every invocation, while the test
reconfigures it again in the next iteration. This leads to repeated
allocation and freeing of large numbers of hugepages, especially when
the original value is high.

Additionally, with set -e, failures in earlier cleanup steps (e.g.,
rmdir or umount returning EBUSY while background activity is still
ongoing) can cause the script to exit before restoring the original
value, leaving the system in a modified state.

Use an EXIT trap to restore the original nr_hugepages once at
script termination. This avoids unnecessary allocation churn and
ensures the original value is reliably restored on all exit paths.

Fixes: 7d695b1c3695b ("selftests/mm: save and restore nr_hugepages value")
Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
---
 tools/testing/selftests/mm/charge_reserved_hugetlb.sh | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
index 447769657634..ca33ec83ebf2 100755
--- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
+++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
@@ -12,6 +12,7 @@ if [[ $(id -u) -ne 0 ]]; then
 fi
 
 nr_hugepgs=$(cat /proc/sys/vm/nr_hugepages)
+trap 'echo "$nr_hugepgs" > /proc/sys/vm/nr_hugepages' EXIT
 
 fault_limit_file=limit_in_bytes
 reservation_limit_file=rsvd.limit_in_bytes
@@ -65,7 +66,6 @@ function cleanup() {
   if [[ -e $cgroup_path/hugetlb_cgroup_test2 ]]; then
     rmdir $cgroup_path/hugetlb_cgroup_test2
   fi
-  echo 0 >/proc/sys/vm/nr_hugepages
   echo CLEANUP DONE
 }
 
@@ -594,4 +594,3 @@ if [[ $do_umount ]]; then
   rmdir $cgroup_path
 fi
 
-echo "$nr_hugepgs" > /proc/sys/vm/nr_hugepages
-- 
2.52.0