[PATCH] selftests/cgroup: test_zswap: skip test_no_kmem_bypass if debugfs is unavailable

[Wilson Felipe Pereira <wfelipe@google.com>]

test_no_kmem_bypass() needs to read
/sys/kernel/debug/zswap/stored_pages via get_zswap_stored_pages() to
verify that compressed pages are charged to the memcg.

When running in an environment where debugfs is not mounted or
CONFIG_DEBUG_FS is disabled, get_zswap_stored_pages() fails, causing the
loop to terminate early and report a false negative (KSFT_FAIL).

Selftests should not fail when if debugfs is unavailable, and it
should print a message when it is skipped.

Signed-off-by: Wilson Felipe Pereira <wfelipe@google.com>
---
 tools/testing/selftests/cgroup/test_zswap.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 49b36ee791606..c4f7b66f1b206 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -566,12 +566,19 @@ static int test_no_kmem_bypass(const char *root)
 	int child_status;
 	char *test_group = NULL;
 	pid_t child_pid;
+	size_t stored_pages;
 
 	/* Read sys info and compute test values accordingly */
 	if (sysinfo(&sys_info) != 0)
 		return KSFT_FAIL;
-	if (sys_info.totalram > 5000000000)
+	if (sys_info.totalram > 5000000000) {
+		ksft_print_msg("requires less than 5000000000 total ram\n");
 		return KSFT_SKIP;
+	}
+	if (get_zswap_stored_pages(&stored_pages)) {
+		ksft_print_msg("debugfs at /sys/kernel/debug is required\n");
+		return KSFT_SKIP;
+	}
 	values = mmap(0, sizeof(struct no_kmem_bypass_child_args), PROT_READ |
 			PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
 	if (values == MAP_FAILED)
@@ -604,7 +611,6 @@ static int test_no_kmem_bypass(const char *root)
 	/* Try to wakeup kswapd and let it push child memory to zswap */
 	set_min_free_kb(min_free_kb_high);
 	for (int i = 0; i < 20; i++) {
-		size_t stored_pages;
 		char *trigger_allocation = malloc(trigger_allocation_size);
 
 		if (!trigger_allocation)
-- 
2.55.0.508.g3f0d502094-goog