selftests/bpf: Unmount the cgroup2 work directory

test_progs -t bind_perm,bpf_obj_pinning/mounted-str-rel fails when
the selftests directory is mounted under /mnt, which is a reasonable
thing to do when sharing the selftests residing on the host with a
virtual machine, e.g., using 9p.

The reason is that cgroup2 is mounted at /mnt and not unmounted,
causing subsequent tests that need to access the selftests directory
to fail.

Fix by unmounting it. The kernel maintains a mount stack, so this
reveals what was mounted there before. Introduce cgroup_workdir_mounted
in order to maintain idempotency. Make it thread-local in order to
support test_progs -j.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230919101336.2223655-3-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c
index 2caee8423ee0229dce5b9789a9cb94f8e4b8f66d..24ba56d42f2dd88d9b9984cc053e2dcc884acd8e 100644 (file)
--- a/tools/testing/selftests/bpf/cgroup_helpers.c
+++ b/tools/testing/selftests/bpf/cgroup_helpers.c
@@ -49,6 +49,10 @@
        snprintf(buf, sizeof(buf), "%s%s", NETCLS_MOUNT_PATH,   \
                 CGROUP_WORK_DIR)
 
+static __thread bool cgroup_workdir_mounted;
+
+static void __cleanup_cgroup_environment(void);
+
 static int __enable_controllers(const char *cgroup_path, const char *controllers)
 {
        char path[PATH_MAX + 1];
@@ -209,9 +213,10 @@ int setup_cgroup_environment(void)
                log_err("mount cgroup2");
                return 1;
        }
+       cgroup_workdir_mounted = true;
 
        /* Cleanup existing failed runs, now that the environment is setup */
-       cleanup_cgroup_environment();
+       __cleanup_cgroup_environment();
 
        if (mkdir(cgroup_workdir, 0777) && errno != EEXIST) {
                log_err("mkdir cgroup work dir");
@@ -305,11 +310,26 @@ int join_parent_cgroup(const char *relative_path)
        return join_cgroup_from_top(cgroup_path);
 }
 
+/**
+ * __cleanup_cgroup_environment() - Delete temporary cgroups
+ *
+ * This is a helper for cleanup_cgroup_environment() that is responsible for
+ * deletion of all temporary cgroups that have been created during the test.
+ */
+static void __cleanup_cgroup_environment(void)
+{
+       char cgroup_workdir[PATH_MAX + 1];
+
+       format_cgroup_path(cgroup_workdir, "");
+       join_cgroup_from_top(CGROUP_MOUNT_PATH);
+       nftw(cgroup_workdir, nftwfunc, WALK_FD_LIMIT, FTW_DEPTH | FTW_MOUNT);
+}
+
 /**
  * cleanup_cgroup_environment() - Cleanup Cgroup Testing Environment
  *
  * This is an idempotent function to delete all temporary cgroups that
- * have been created during the test, including the cgroup testing work
+ * have been created during the test and unmount the cgroup testing work
  * directory.
  *
  * At call time, it moves the calling process to the root cgroup, and then
@@ -320,11 +340,10 @@ int join_parent_cgroup(const char *relative_path)
  */
 void cleanup_cgroup_environment(void)
 {
-       char cgroup_workdir[PATH_MAX + 1];
-
-       format_cgroup_path(cgroup_workdir, "");
-       join_cgroup_from_top(CGROUP_MOUNT_PATH);
-       nftw(cgroup_workdir, nftwfunc, WALK_FD_LIMIT, FTW_DEPTH | FTW_MOUNT);
+       __cleanup_cgroup_environment();
+       if (cgroup_workdir_mounted && umount(CGROUP_MOUNT_PATH))
+               log_err("umount cgroup2");
+       cgroup_workdir_mounted = false;
 }
 
 /**