run_hugetlbfs_test.sh in memfd of ubuntu_kernel_selftests causing sut-test failure on J-6.8

[Po-Hsu Lin]

Found on Jammy 6.8 variants since 2024.04.29:
  * J-oracle-6.8.0-1006.6~22.04.3 (2024.04.29)
  * J-azure-6.8.0-1008.8~22.04.1 (2024.04.29)
  * J-aws-6.8.0-1009.9~22.04.2 (2024.04.29)
  * J-gcp-6.8.0-1010.11~22.04.1 (2024.06.10)
  * J-hwe-6.8.0-38.38~22.04.1 (2024.06.10)
  * J-ibm-6.8.0-1008.8~22.04.1 (2024.06.10)
  * J-lowlatency-hwe-6.8.0-38.38.1~22.04.2 (2024.06.10)
  * J-nvidia-6.8.0-1009.9~22.04.1 (2024.06.10)
  * J-realtime-6.8.1-1004.4~22.04.1 (2024.06.10)

When trying to run the memfd test in ubuntu_kernel_selftests, the run_hugetlbfs_test.sh sub-test will have a leftover process the prevents the test to finish properly, and consequently causing sut-test failure in our infrastructure.

$ cd ~/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/
$ sudo make TARGETS=memfd
$ cd memfd
$ sudo ./run_hugetlbfs_test.sh
memfd-hugetlb: CREATE
memfd-hugetlb: BASIC
memfd-hugetlb: SEAL-EXEC
memfd-hugetlb: Apply SEAL_EXEC
fchmod(/memfd:kern_memfd_seal_exec (deleted), 00777) didn't fail as expected
./run_hugetlbfs_test.sh: line 60: 1424 Aborted (core dumped) ./memfd_test hugetlbfs
fusermount: failed to unmount /home/ubuntu/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/memfd/mnt: Invalid argument
eopening: ./mnt/memfd
cho $?ADD_SEALS(4, 0 -> 8) failed: Device or resource busy
8 != 0 = GET_SEALS(4)
Aborted (core dumped)
$ echo $?
0
$ ps aux | grep fuse
root 1431 0.0 0.0 150776 1292 ? Ssl 01:50 0:00 ./fuse_mnt ./mnt
ubuntu 1454 0.0 0.0 7008 2304 pts/0 S+ 01:50 0:00 grep --color=auto fuse

$ sudo strace -p 1431
strace: Process 1431 attached
futex(0x7fff9738a3f0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, FUTEX_BITSET_MATCH_ANY
^C

Nothing interesting in dmesg output.

[Po-Hsu Lin (cypressyew)]

This is not affect Noble 6.8, despite the test output is identical:

 Running 'make run_tests -C memfd TEST_PROGS=run_hugetlbfs_test.sh TEST_GEN_PROGS='' TEST_CUSTOM_PROGS='''
 make: Entering directory '/home/ubuntu/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/memfd'
 TAP version 13
 1..1
 # timeout set to 45
 # selftests: memfd: run_hugetlbfs_test.sh
 # memfd-hugetlb: CREATE
 # memfd-hugetlb: BASIC
 # memfd-hugetlb: SEAL-EXEC
 # memfd-hugetlb: Apply SEAL_EXEC
 # fchmod(/memfd:kern_memfd_seal_exec (deleted), 00777) didn't fail as expected
 # ./run_hugetlbfs_test.sh: line 60: 15915 Aborted (core dumped) ./memfd_test hugetlbfs
 # opening: ./mnt/memfd
 # ADD_SEALS(6, 0 -> 8) failed: Device or resource busy
 # 8 != 0 = GET_SEALS(6)
 # Aborted (core dumped)
 ok 1 selftests: memfd: run_hugetlbfs_test.sh