From: Tejun Heo Date: Tue, 24 Mar 2026 20:21:47 +0000 (-1000) Subject: selftests/cgroup: Don't require synchronous populated update on task exit X-Git-Tag: v7.0-rc7~34^2~3 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=6680c162b4850976ee52b57372eddc4450c1d074;p=thirdparty%2Fkernel%2Flinux.git 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(). 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 Signed-off-by: Tejun Heo Tested-by: Sebastian Andrzej Siewior Cc: Christian Brauner Cc: cgroups@vger.kernel.org --- diff --git a/tools/testing/selftests/cgroup/lib/cgroup_util.c b/tools/testing/selftests/cgroup/lib/cgroup_util.c index ce6c2642fd9bb..6a7295347e90b 100644 --- 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, 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]; diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h index 77f386dab5e8f..567b1082974c5 100644 --- 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, 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); diff --git a/tools/testing/selftests/cgroup/test_core.c b/tools/testing/selftests/cgroup/test_core.c index 102262555a599..7b83c7e7c9d4f 100644 --- 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 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. */ diff --git a/tools/testing/selftests/cgroup/test_kill.c b/tools/testing/selftests/cgroup/test_kill.c index c8c9d306925b6..f6cd23a8ecc71 100644 --- 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)