ksm02 ksm02_1 ksm03 ksm03_1 ksm04 ksm04_1 failed on KVM kernels

[Po-Hsu Lin]

Issue found on E-KVM 5.3.0-1025.27 - kvm

It will fail with:
 tag=ksm02 stime=1594129854 dur=5 exit=exited stat=34 core=no cu=0 cs=0
 startup='Tue Jul 7 13:50:54 2020'
 tst_sys_conf.c:58: INFO: Path not found: '/sys/kernel/mm/ksm/max_page_sharing'
 tst_test.c:1247: INFO: Timeout per run is 0h 05m 00s
 ksm02.c:96: CONF: KSM configuration is not enabled
 tst_device.c:418: INFO: No device is mounted at /tmp/cgroup_cst
 tst_test.c:1292: BROK: Test killed by SIGSEGV!

 Summary:
 passed 0
 failed 0
 skipped 1
 warnings 0

These tests will require CONFIG_KSM set to y, which we don't have in KVM kernels.

And these tests are smart enough to check for this config on the fly:
  if (access(PATH_KSM, F_OK) == -1)
    tst_brk(TCONF, "KSM configuration is not enabled");

Therefore we don't need to blacklist it in our test suite.

For example the ksm01 test will be skipped correctly:
startup='Fri Jul 3 16:11:37 2020'
tst_sys_conf.c:58: INFO: Path not found: '/sys/kernel/mm/ksm/max_page_sharing'
tst_test.c:1245: INFO: Timeout per run is 0h 05m 00s
ksm01.c:70: CONF: KSM configuration is not enabled

Summary:
passed 0
failed 0
skipped 1
warnings 0
tag=ksm01 stime=1593792697 dur=0 exit=exited stat=32 core=no cu=0 cs=0

After investigating the test code more carefully, it's failing because of the cleanup code, which tried to unmount a dir that's not mounted. And thus causing failures like:
 tst_device.c:418: INFO: No device is mounted at /tmp/cgroup_cst
 tst_test.c:1292: BROK: Test killed by SIGSEGV!

Making tests being marked as failed.

[Po-Hsu Lin (cypressyew)]

Inside the test code of ltp/testcases/kernel/mem/ksm/ksm02.c, it's failing in:
    tst_cgroup_umount(PATH_TMP_CG_CST);

Which is doing two things in ltp/lib/tst_cgroup.c:
    tst_cgroupN_umount(cgroup_dir, cgroup_new_dir);
    tst_cgroup_del_path(cgroup_dir);

The tst_cgroupN_umount() here will check if the mount point has been mounted or not:
    if (!tst_is_mounted(mnt_path))
        return;

Therefore you will see the following message printed:
 tst_device.c:418: INFO: No device is mounted at /tmp/cgroup_cst

So it's failing in tst_cgroup_del_path().

[Po-Hsu Lin (cypressyew)]

It's because the tst_cgroup_paths in tst_cgroup_del_path() is NULL, it should be skipped in this case.

[Po-Hsu Lin (cypressyew)]

Patch applied.

https://github.com/linux-test-project/ltp/commit/b60a171bfa33b6cba38104163692fd205f45bfdf

Tested on Focal KVM, it works as expected.