Merge branch 'Introduce a new kfunc of bpf_task_under_cgroup'

Feng zhou says:

====================
Trace sched related functions, such as enqueue_task_fair, it is necessary to
specify a task instead of the current task which within a given cgroup.
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/helpers.c

@@ -2149,6 +2149,22 @@ __bpf_kfunc struct cgroup *bpf_cgroup_from_id(u64 cgid)
 		return NULL;
 	return cgrp;
 }
+
+/**
+ * bpf_task_under_cgroup - wrap task_under_cgroup_hierarchy() as a kfunc, test
+ * task's membership of cgroup ancestry.
+ * @task: the task to be tested
+ * @ancestor: possible ancestor of @task's cgroup
+ *
+ * Tests whether @task's default cgroup hierarchy is a descendant of @ancestor.
+ * It follows all the same rules as cgroup_is_descendant, and only applies
+ * to the default hierarchy.
+ */
+__bpf_kfunc long bpf_task_under_cgroup(struct task_struct *task,
+				       struct cgroup *ancestor)
+{
+	return task_under_cgroup_hierarchy(task, ancestor);
+}
 #endif /* CONFIG_CGROUPS */
 
 /**
@@ -2400,6 +2416,7 @@ BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_cgroup_release, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_cgroup_from_id, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_task_under_cgroup, KF_RCU)
 #endif
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
 BTF_SET8_END(generic_btf_ids)

tools/testing/selftests/bpf/DENYLIST.s390x

@@ -26,3 +26,4 @@ user_ringbuf                             # failed to find kernel BTF type ID of
 verif_stats                              # trace_vprintk__open_and_load unexpected error: -9                           (?)
 xdp_bonding                              # failed to auto-attach program 'trace_on_entry': -524                        (trampoline)
 xdp_metadata                             # JIT does not support calling kernel function                                (kfunc)
+test_task_under_cgroup                   # JIT does not support calling kernel function                                (kfunc)

tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Bytedance */
+
+#include <sys/syscall.h>
+#include <test_progs.h>
+#include <cgroup_helpers.h>
+#include "test_task_under_cgroup.skel.h"
+
+#define FOO	"/foo"
+
+void test_task_under_cgroup(void)
+{
+	struct test_task_under_cgroup *skel;
+	int ret, foo;
+	pid_t pid;
+
+	foo = test__join_cgroup(FOO);
+	if (!ASSERT_OK(foo < 0, "cgroup_join_foo"))
+		return;
+
+	skel = test_task_under_cgroup__open();
+	if (!ASSERT_OK_PTR(skel, "test_task_under_cgroup__open"))
+		goto cleanup;
+
+	skel->rodata->local_pid = getpid();
+	skel->bss->remote_pid = getpid();
+	skel->rodata->cgid = get_cgroup_id(FOO);
+
+	ret = test_task_under_cgroup__load(skel);
+	if (!ASSERT_OK(ret, "test_task_under_cgroup__load"))
+		goto cleanup;
+
+	ret = test_task_under_cgroup__attach(skel);
+	if (!ASSERT_OK(ret, "test_task_under_cgroup__attach"))
+		goto cleanup;
+
+	pid = fork();
+	if (pid == 0)
+		exit(0);
+
+	ret = (pid == -1);
+	if (ASSERT_OK(ret, "fork process"))
+		wait(NULL);
+
+	test_task_under_cgroup__detach(skel);
+
+	ASSERT_NEQ(skel->bss->remote_pid, skel->rodata->local_pid,
+		   "test task_under_cgroup");
+
+cleanup:
+	test_task_under_cgroup__destroy(skel);
+	close(foo);
+}

tools/testing/selftests/bpf/progs/test_task_under_cgroup.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Bytedance */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+#include "bpf_misc.h"
+
+struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
+long bpf_task_under_cgroup(struct task_struct *task, struct cgroup *ancestor) __ksym;
+void bpf_cgroup_release(struct cgroup *p) __ksym;
+struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
+void bpf_task_release(struct task_struct *p) __ksym;
+
+const volatile int local_pid;
+const volatile __u64 cgid;
+int remote_pid;
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(handle__task_newtask, struct task_struct *task, u64 clone_flags)
+{
+	struct cgroup *cgrp = NULL;
+	struct task_struct *acquired;
+
+	if (local_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	acquired = bpf_task_acquire(task);
+	if (!acquired)
+		return 0;
+
+	if (local_pid == acquired->tgid)
+		goto out;
+
+	cgrp = bpf_cgroup_from_id(cgid);
+	if (!cgrp)
+		goto out;
+
+	if (bpf_task_under_cgroup(acquired, cgrp))
+		remote_pid = acquired->tgid;
+
+out:
+	if (cgrp)
+		bpf_cgroup_release(cgrp);
+	bpf_task_release(acquired);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";