Commit 6680c162 authored by Tejun Heo's avatar Tejun Heo
Browse files

selftests/cgroup: Don't require synchronous populated update on task exit 



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().

d245698d ("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: d245698d ("cgroup: Defer task cgroup unlink until after the task is done switching out")
Reported-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Tested-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: cgroups@vger.kernel.org
parent 1b164b87

tools/testing/selftests/cgroup/lib/cgroup_util.c

+15 −0
Original line number Diff line number Diff line
@@ -123,6 +123,21 @@ int cg_read_strcmp(const char *cgroup, const char *control, 
	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];

tools/testing/selftests/cgroup/lib/include/cgroup_util.h

+2 −0
Original line number Diff line number Diff line
@@ -61,6 +61,8 @@ extern int cg_read(const char *cgroup, const char *control, 
		   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);

tools/testing/selftests/cgroup/test_core.c

+2 −1
Original line number Diff line number Diff line
@@ -233,7 +233,8 @@ static int test_cgcore_populated(const char *root) 
	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. */

tools/testing/selftests/cgroup/test_kill.c

+4 −3
Original line number Diff line number Diff line
@@ -86,7 +86,7 @@ static int test_cgkill_simple(const char *root) 
		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 @@ static int test_cgkill_tree(const char *root) 
		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 @@ static int test_cgkill_forkbomb(const char *root) 
		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)