Re: [PATCH 04/11] sched_ext: Fix processs_ddsp_deferred_locals() by unifying DTL_INVALID handling

[David Vernet]

On Sat, Aug 31, 2024 at 10:03:58PM -1000, Tejun Heo wrote:
> Hello,
> 
> On Sat, Aug 31, 2024 at 07:56:39PM -0500, David Vernet wrote:
> ...
> > Sorry, should have been more clear: the testcase dispatched all tasks to
> > the wrong CPU, which is why it's a kworker in the print output below. I
> > believe that ksoftiqrd hit the same path as well and just wasn't printed
> > in the output because it lost the race to scx_bpf_error(). Let me know
> > if you want the testcase to repro and I can send it, or send a separate
> > patch to add it to selftests.
> 
> Yeah, please share the repro.

See the attached patch. You can run the test as follows after rebuilding
selftests:

./runner -t ddsp_local_on_invalid

You may have to run the test a few times to see the repro. Worth noting
is that the repro doesn't seem to hit if we don't explicitly set the
fallback target to 0 in ddsp_local_on_invalid_enqueue().

Thanks,
David
From 5e1a850b7db989429b94ea5d9cdf786faf3bcd4f Mon Sep 17 00:00:00 2001
From: David Vernet <void@xxxxxxxxxxxxx>
Date: Sat, 31 Aug 2024 19:16:22 -0500
Subject: [PATCH] scx: Add test validating direct dispatch with LOCAL_ON

SCX_DSQ_LOCAL_ON | cpu can now be invoked on the direct dispatch path.
Let's ensure we're gracefully handling it being dispatched to a CPU
that it's not allowed to run on.

Signed-off-by: David Vernet <void@xxxxxxxxxxxxx>
---
 tools/testing/selftests/sched_ext/Makefile    |  1 +
 .../sched_ext/ddsp_local_on_invalid.bpf.c     | 42 ++++++++++++++
 .../sched_ext/ddsp_local_on_invalid.c         | 58 +++++++++++++++++++
 3 files changed, 101 insertions(+)
 create mode 100644 tools/testing/selftests/sched_ext/ddsp_local_on_invalid.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/ddsp_local_on_invalid.c

diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 0754a2c110a1..4823a67e6854 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -165,6 +165,7 @@ auto-test-targets :=			\
 	enq_last_no_enq_fails		\
 	enq_select_cpu_fails		\
 	ddsp_bogus_dsq_fail		\
+	ddsp_local_on_invalid		\
 	ddsp_vtimelocal_fail		\
 	dsp_local_on			\
 	exit				\
diff --git a/tools/testing/selftests/sched_ext/ddsp_local_on_invalid.bpf.c b/tools/testing/selftests/sched_ext/ddsp_local_on_invalid.bpf.c
new file mode 100644
index 000000000000..e4512d7cc4b5
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/ddsp_local_on_invalid.bpf.c
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@xxxxxxxx>
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+const volatile s32 nr_cpus;
+
+UEI_DEFINE(uei);
+
+s32 BPF_STRUCT_OPS(ddsp_local_on_invalid_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(ddsp_local_on_invalid_enqueue, struct task_struct *p,
+		    u64 enq_flags)
+{
+	int target = bpf_cpumask_first_zero(p->cpus_ptr);
+
+	if (target >= nr_cpus)
+		target = 0;
+
+	scx_bpf_dispatch(p, SCX_DSQ_LOCAL_ON | target, SCX_SLICE_DFL, enq_flags);
+}
+
+void BPF_STRUCT_OPS(ddsp_local_on_invalid_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops ddsp_local_on_invalid_ops = {
+	.select_cpu		= ddsp_local_on_invalid_select_cpu,
+	.enqueue		= ddsp_local_on_invalid_enqueue,
+	.exit			= ddsp_local_on_invalid_exit,
+	.name			= "ddsp_local_on_invalid",
+	.timeout_ms		= 2000U,
+};
diff --git a/tools/testing/selftests/sched_ext/ddsp_local_on_invalid.c b/tools/testing/selftests/sched_ext/ddsp_local_on_invalid.c
new file mode 100644
index 000000000000..7bc49df06ee0
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/ddsp_local_on_invalid.c
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@xxxxxxxx>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <unistd.h>
+#include "ddsp_local_on_invalid.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct ddsp_local_on_invalid *skel;
+
+	skel = ddsp_local_on_invalid__open();
+	SCX_FAIL_IF(!skel, "Failed to open");
+
+	skel->rodata->nr_cpus = libbpf_num_possible_cpus();
+	SCX_FAIL_IF(ddsp_local_on_invalid__load(skel), "Failed to load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct ddsp_local_on_invalid *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.ddsp_local_on_invalid_ops);
+	SCX_FAIL_IF(!link, "Failed to attach struct_ops");
+
+	/* Just sleeping is fine, plenty of scheduling events happening */
+	sleep(1);
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_ERROR));
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct ddsp_local_on_invalid *skel = ctx;
+
+	ddsp_local_on_invalid__destroy(skel);
+}
+
+struct scx_test ddsp_local_on_invalid = {
+	.name = "ddsp_local_on_invalid",
+	.description = "Verify we can gracefully handle direct dispatch "
+		       "of tasks to an invalid local DSQ from osp.dispatch()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&ddsp_local_on_invalid)
-- 
2.45.2

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