[PATCH v2 bpf-next 4/4] selftests/bpf: Add test for sleepable bpf iterator programs

[Kenny Yu <kennyyu@fb.com>]

This adds a test for bpf iterator programs to make use of sleepable
bpf helpers.

Signed-off-by: Kenny Yu <kennyyu@fb.com>
---
 .../selftests/bpf/prog_tests/bpf_iter.c       | 16 ++++++
 .../selftests/bpf/progs/bpf_iter_task.c       | 54 +++++++++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index b84f859b1267..fcda0ecd8746 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -138,6 +138,20 @@ static void test_task(void)
 	bpf_iter_task__destroy(skel);
 }
 
+static void test_task_sleepable(void)
+{
+	struct bpf_iter_task *skel;
+
+	skel = bpf_iter_task__open_and_load();
+	if (CHECK(!skel, "bpf_iter_task__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	do_dummy_read(skel->progs.dump_task_sleepable);
+
+	bpf_iter_task__destroy(skel);
+}
+
 static void test_task_stack(void)
 {
 	struct bpf_iter_task_stack *skel;
@@ -1252,6 +1266,8 @@ void test_bpf_iter(void)
 		test_bpf_map();
 	if (test__start_subtest("task"))
 		test_task();
+	if (test__start_subtest("task_sleepable"))
+		test_task_sleepable();
 	if (test__start_subtest("task_stack"))
 		test_task_stack();
 	if (test__start_subtest("task_file"))
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task.c b/tools/testing/selftests/bpf/progs/bpf_iter_task.c
index c86b93f33b32..bb4b63043533 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter_task.c
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task.c
@@ -2,6 +2,7 @@
 /* Copyright (c) 2020 Facebook */
 #include "bpf_iter.h"
 #include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
 
 char _license[] SEC("license") = "GPL";
 
@@ -23,3 +24,56 @@ int dump_task(struct bpf_iter__task *ctx)
 	BPF_SEQ_PRINTF(seq, "%8d %8d\n", task->tgid, task->pid);
 	return 0;
 }
+
+// New helper added
+static long (*bpf_access_process_vm)(
+	struct task_struct *tsk,
+	unsigned long addr,
+	void *buf,
+	int len,
+	unsigned int gup_flags) = (void *)186;
+
+// Copied from include/linux/mm.h
+#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
+
+SEC("iter.s/task")
+int dump_task_sleepable(struct bpf_iter__task *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	static const char info[] = "    === END ===";
+	struct pt_regs *regs;
+	void *ptr;
+	uint32_t user_data = 0;
+	int numread;
+
+	if (task == (void *)0) {
+		BPF_SEQ_PRINTF(seq, "%s\n", info);
+		return 0;
+	}
+
+	regs = (struct pt_regs *)bpf_task_pt_regs(task);
+	if (regs == (void *)0) {
+		BPF_SEQ_PRINTF(seq, "%s\n", info);
+		return 0;
+	}
+	ptr = (void *)PT_REGS_IP(regs);
+
+	// Try to read the contents of the task's instruction pointer from the
+	// remote task's address space.
+	numread = bpf_access_process_vm(task,
+					(unsigned long)ptr,
+					(void *)&user_data,
+					sizeof(uint32_t),
+					FOLL_REMOTE);
+	if (numread != sizeof(uint32_t)) {
+		BPF_SEQ_PRINTF(seq, "%s\n", info);
+		return 0;
+	}
+
+	if (ctx->meta->seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "    tgid      gid     data\n");
+
+	BPF_SEQ_PRINTF(seq, "%8d %8d %8d\n", task->tgid, task->pid, user_data);
+	return 0;
+}
-- 
2.30.2