Once cgroup.kill had been written to a cgroup, a stale kill_seq snapshot (taken in cgroup_css_set_fork() before the target cgroup was resolved) caused every child subsequently cloned into that cgroup with clone3(CLONE_INTO_CGROUP) to be SIGKILLed on the spot.
Add a regression test: create a cgroup, kill it while it is empty, then clone a child into it and check that the child runs and exits cleanly. On a kernel without the fix, the test fails: not ok 4 test_cgkill_clone_into_killed The test is skipped on kernels without clone3() or without CLONE_INTO_CGROUP. Cc: Shakeel Butt <[email protected]> Assisted-by: LLM Signed-off-by: Etienne Perot <[email protected]> --- tools/testing/selftests/cgroup/test_kill.c | 55 ++++++++++++++++++++++ 1 file changed, 55 insertions(+) diff --git a/tools/testing/selftests/cgroup/test_kill.c b/tools/testing/selftests/cgroup/test_kill.c index f6cd23a8ecc7..5ba8e285b2f3 100644 --- a/tools/testing/selftests/cgroup/test_kill.c +++ b/tools/testing/selftests/cgroup/test_kill.c @@ -7,6 +7,7 @@ #include <stdlib.h> #include <string.h> #include <sys/types.h> +#include <sys/wait.h> #include <unistd.h> #include "kselftest.h" @@ -261,6 +262,59 @@ static int test_cgkill_forkbomb(const char *root) return ret; } +/* + * Test that a cgroup that was killed in the past can still be the target + * of clone3(CLONE_INTO_CGROUP): writing cgroup.kill must only kill the + * tasks in the cgroup at the time of the write, not tasks cloned into + * it afterwards. + */ +static int test_cgkill_clone_into_killed(const char *root) +{ + pid_t pid; + int cgroup_fd = -EBADF; + int ret = KSFT_FAIL; + char *cgroup = NULL; + + cgroup = cg_name(root, "cg_test_clone_into_killed"); + if (!cgroup) + goto cleanup; + + if (cg_create(cgroup)) + goto cleanup; + + /* Kill the cgroup while it is still empty. */ + if (cg_write(cgroup, "cgroup.kill", "1")) + goto cleanup; + + cgroup_fd = dirfd_open_opath(cgroup); + if (cgroup_fd < 0) + goto cleanup; + + pid = clone_into_cgroup(cgroup_fd); + if (pid < 0) { + if (errno == ENOSYS) + ret = KSFT_SKIP; + goto cleanup; + } + + if (pid == 0) + exit(EXIT_SUCCESS); + + /* The child must not be SIGKILLed; it has to exit cleanly. */ + if (clone_reap(pid, WEXITED) != EXIT_SUCCESS) + goto cleanup; + + ret = KSFT_PASS; + +cleanup: + if (cgroup_fd >= 0) + close(cgroup_fd); + if (cgroup) + cg_destroy(cgroup); + free(cgroup); + return ret; +} + #define T(x) { x, #x } struct cgkill_test { int (*fn)(const char *root); @@ -269,6 +323,7 @@ struct cgkill_test { T(test_cgkill_simple), T(test_cgkill_tree), T(test_cgkill_forkbomb), + T(test_cgkill_clone_into_killed), }; #undef T -- 2.55.0.897.gb25b4bd76c-goog
