test_cgcore_populated (test_core) and test_cgkill_{simple,tree,forkbomb}
(test_kill) check cgroup.events "populated 0" immediately after reaping
child tasks with waitpid(). This used to work because cgroup_task_exit() in
do_exit() unlinked tasks from css_sets before exit_notify() woke up
waitpid().
d245698d727a ("cgroup: Defer task cgroup unlink until after the task is done
switching out") moved the unlink to cgroup_task_dead() in
finish_task_switch(), which runs after exit_notify(). The populated counter
is now decremented after the parent's waitpid() can return, so there is no
longer a synchronous ordering guarantee. On PREEMPT_RT, where
cgroup_task_dead() is further deferred through lazy irq_work, the race
window is even larger.
The synchronous populated transition was never part of the cgroup interface
contract - it was an implementation artifact. Use cg_read_strcmp_wait() which
retries for up to 1 second, matching what these tests actually need to
verify: that the cgroup eventually becomes unpopulated after all tasks exit.
Fixes: d245698d727a ("cgroup: Defer task cgroup unlink until after the task is
done switching out")
Reported-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: [email protected]
---
tools/testing/selftests/cgroup/lib/cgroup_util.c | 15 +++++++++++++++
tools/testing/selftests/cgroup/lib/include/cgroup_util.h | 2 ++
tools/testing/selftests/cgroup/test_core.c | 3 ++-
tools/testing/selftests/cgroup/test_kill.c | 7 ++++---
4 files changed, 23 insertions(+), 4 deletions(-)
--- a/tools/testing/selftests/cgroup/lib/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/lib/cgroup_util.c
@@ -123,6 +123,21 @@ int cg_read_strcmp(const char *cgroup, c
return ret;
}
+int cg_read_strcmp_wait(const char *cgroup, const char *control,
+ const char *expected)
+{
+ int i, ret;
+
+ for (i = 0; i < 100; i++) {
+ ret = cg_read_strcmp(cgroup, control, expected);
+ if (!ret)
+ return ret;
+ usleep(10000);
+ }
+
+ return ret;
+}
+
int cg_read_strstr(const char *cgroup, const char *control, const char *needle)
{
char buf[PAGE_SIZE];
--- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
@@ -61,6 +61,8 @@ extern int cg_read(const char *cgroup, c
char *buf, size_t len);
extern int cg_read_strcmp(const char *cgroup, const char *control,
const char *expected);
+extern int cg_read_strcmp_wait(const char *cgroup, const char *control,
+ const char *expected);
extern int cg_read_strstr(const char *cgroup, const char *control,
const char *needle);
extern long cg_read_long(const char *cgroup, const char *control);
--- a/tools/testing/selftests/cgroup/test_core.c
+++ b/tools/testing/selftests/cgroup/test_core.c
@@ -233,7 +233,8 @@ static int test_cgcore_populated(const c
if (err)
goto cleanup;
- if (cg_read_strcmp(cg_test_d, "cgroup.events", "populated 0\n"))
+ if (cg_read_strcmp_wait(cg_test_d, "cgroup.events",
+ "populated 0\n"))
goto cleanup;
/* Remove cgroup. */
--- a/tools/testing/selftests/cgroup/test_kill.c
+++ b/tools/testing/selftests/cgroup/test_kill.c
@@ -86,7 +86,7 @@ cleanup:
wait_for_pid(pids[i]);
if (ret == KSFT_PASS &&
- cg_read_strcmp(cgroup, "cgroup.events", "populated 0\n"))
+ cg_read_strcmp_wait(cgroup, "cgroup.events", "populated 0\n"))
ret = KSFT_FAIL;
if (cgroup)
@@ -190,7 +190,8 @@ cleanup:
wait_for_pid(pids[i]);
if (ret == KSFT_PASS &&
- cg_read_strcmp(cgroup[0], "cgroup.events", "populated 0\n"))
+ cg_read_strcmp_wait(cgroup[0], "cgroup.events",
+ "populated 0\n"))
ret = KSFT_FAIL;
for (i = 9; i >= 0 && cgroup[i]; i--) {
@@ -251,7 +252,7 @@ cleanup:
wait_for_pid(pid);
if (ret == KSFT_PASS &&
- cg_read_strcmp(cgroup, "cgroup.events", "populated 0\n"))
+ cg_read_strcmp_wait(cgroup, "cgroup.events", "populated 0\n"))
ret = KSFT_FAIL;
if (cgroup)
