[PATCH v3 bpf-next 0/2] introduce BPF_F_PRESERVE_ELEMS

[PATCH v3 bpf-next 0/2] introduce BPF_F_PRESERVE_ELEMS

[Song Liu]

This set introduces BPF_F_PRESERVE_ELEMS to perf event array for better
sharing of perf event. By default, perf event array removes the perf event
when the map fd used to add the event is closed. With BPF_F_PRESERVE_ELEMS
set, however, the perf event will stay in the array until it is removed, or
the map is closed.

---
Changes v2 => v3:
1. Move perf_event_fd_array_map_free() to avoid unnecessary forward
   declaration. (Daniel)

Changes v1 => v2:
1. Rename the flag as BPF_F_PRESERVE_ELEMS. (Alexei, Daniel)
2. Simplify the code and selftest. (Daniel, Alexei)

Song Liu (2):
  bpf: introduce BPF_F_PRESERVE_ELEMS for perf event array
  selftests/bpf: add tests for BPF_F_PRESERVE_ELEMS

 include/uapi/linux/bpf.h                      |  3 +
 kernel/bpf/arraymap.c                         | 19 +++++-
 tools/include/uapi/linux/bpf.h                |  3 +
 .../bpf/prog_tests/pe_preserve_elems.c        | 66 +++++++++++++++++++
 .../bpf/progs/test_pe_preserve_elems.c        | 44 +++++++++++++
 5 files changed, 133 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c

--
2.24.1

[PATCH v3 bpf-next 1/2] bpf: introduce BPF_F_PRESERVE_ELEMS for perf event array

[Song Liu]

Currently, perf event in perf event array is removed from the array when
the map fd used to add the event is closed. This behavior makes it
difficult to the share perf events with perf event array.

Introduce perf event map that keeps the perf event open with a new flag
BPF_F_PRESERVE_ELEMS. With this flag set, perf events in the array are not
removed when the original map fd is closed. Instead, the perf event will
stay in the map until 1) it is explicitly removed from the array; or 2)
the array is freed.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 include/uapi/linux/bpf.h       |  3 +++
 kernel/bpf/arraymap.c          | 19 +++++++++++++++++--
 tools/include/uapi/linux/bpf.h |  3 +++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2b1d3f16cbd1c..98fb54989be78 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -414,6 +414,9 @@ enum {
 
 /* Enable memory-mapping BPF map */
 	BPF_F_MMAPABLE		= (1U << 10),
+
+/* Share perf_event among processes */
+	BPF_F_PRESERVE_ELEMS	= (1U << 11),
 };
 
 /* Flags for BPF_PROG_QUERY. */
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index e5fd31268ae02..bd777dd6f9677 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -15,7 +15,8 @@
 #include "map_in_map.h"
 
 #define ARRAY_CREATE_FLAG_MASK \
-	(BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK)
+	(BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK | \
+	 BPF_F_PRESERVE_ELEMS)
 
 static void bpf_array_free_percpu(struct bpf_array *array)
 {
@@ -64,6 +65,10 @@ int array_map_alloc_check(union bpf_attr *attr)
 	    attr->map_flags & BPF_F_MMAPABLE)
 		return -EINVAL;
 
+	if (attr->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY &&
+	    attr->map_flags & BPF_F_PRESERVE_ELEMS)
+		return -EINVAL;
+
 	if (attr->value_size > KMALLOC_MAX_SIZE)
 		/* if value_size is bigger, the user space won't be able to
 		 * access the elements.
@@ -1134,6 +1139,9 @@ static void perf_event_fd_array_release(struct bpf_map *map,
 	struct bpf_event_entry *ee;
 	int i;
 
+	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
+		return;
+
 	rcu_read_lock();
 	for (i = 0; i < array->map.max_entries; i++) {
 		ee = READ_ONCE(array->ptrs[i]);
@@ -1143,12 +1151,19 @@ static void perf_event_fd_array_release(struct bpf_map *map,
 	rcu_read_unlock();
 }
 
+static void perf_event_fd_array_map_free(struct bpf_map *map)
+{
+	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
+		bpf_fd_array_map_clear(map);
+	fd_array_map_free(map);
+}
+
 static int perf_event_array_map_btf_id;
 const struct bpf_map_ops perf_event_array_map_ops = {
 	.map_meta_equal = bpf_map_meta_equal,
 	.map_alloc_check = fd_array_map_alloc_check,
 	.map_alloc = array_map_alloc,
-	.map_free = fd_array_map_free,
+	.map_free = perf_event_fd_array_map_free,
 	.map_get_next_key = array_map_get_next_key,
 	.map_lookup_elem = fd_array_map_lookup_elem,
 	.map_delete_elem = fd_array_map_delete_elem,
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2b1d3f16cbd1c..98fb54989be78 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -414,6 +414,9 @@ enum {
 
 /* Enable memory-mapping BPF map */
 	BPF_F_MMAPABLE		= (1U << 10),
+
+/* Share perf_event among processes */
+	BPF_F_PRESERVE_ELEMS	= (1U << 11),
 };
 
 /* Flags for BPF_PROG_QUERY. */
-- 
2.24.1

[PATCH v3 bpf-next 2/2] selftests/bpf: add tests for BPF_F_PRESERVE_ELEMS

[Song Liu]

Add tests for perf event array with and without BPF_F_PRESERVE_ELEMS.

Add a perf event to array via fd mfd. Without BPF_F_PRESERVE_ELEMS, the
perf event is removed when mfd is closed. With BPF_F_PRESERVE_ELEMS, the
perf event is removed when the map is freed.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 .../bpf/prog_tests/pe_preserve_elems.c        | 66 +++++++++++++++++++
 .../bpf/progs/test_pe_preserve_elems.c        | 44 +++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c

diff --git a/tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c b/tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
new file mode 100644
index 0000000000000..673d38395253b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2019 Facebook */
+#include <test_progs.h>
+#include <linux/bpf.h>
+#include "test_pe_preserve_elems.skel.h"
+
+static int duration;
+
+static void test_one_map(struct bpf_map *map, struct bpf_program *prog,
+			 bool has_share_pe)
+{
+	int err, key = 0, pfd = -1, mfd = bpf_map__fd(map);
+	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts);
+	struct perf_event_attr attr = {
+		.size = sizeof(struct perf_event_attr),
+		.type = PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_CPU_CLOCK,
+	};
+
+	pfd = syscall(__NR_perf_event_open, &attr, 0 /* pid */,
+		      -1 /* cpu 0 */, -1 /* group id */, 0 /* flags */);
+	if (CHECK(pfd < 0, "perf_event_open", "failed\n"))
+		return;
+
+	err = bpf_map_update_elem(mfd, &key, &pfd, BPF_ANY);
+	close(pfd);
+	if (CHECK(err < 0, "bpf_map_update_elem", "failed\n"))
+		return;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(prog), &opts);
+	if (CHECK(err < 0, "bpf_prog_test_run_opts", "failed\n"))
+		return;
+	if (CHECK(opts.retval != 0, "bpf_perf_event_read_value",
+		  "failed with %d\n", opts.retval))
+		return;
+
+	/* closing mfd, prog still holds a reference on map */
+	close(mfd);
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(prog), &opts);
+	if (CHECK(err < 0, "bpf_prog_test_run_opts", "failed\n"))
+		return;
+
+	if (has_share_pe) {
+		CHECK(opts.retval != 0, "bpf_perf_event_read_value",
+		      "failed with %d\n", opts.retval);
+	} else {
+		CHECK(opts.retval != -ENOENT, "bpf_perf_event_read_value",
+		      "should have failed with %d, but got %d\n", -ENOENT,
+		      opts.retval);
+	}
+}
+
+void test_pe_preserve_elems(void)
+{
+	struct test_pe_preserve_elems *skel;
+
+	skel = test_pe_preserve_elems__open_and_load();
+	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+		return;
+
+	test_one_map(skel->maps.array_1, skel->progs.read_array_1, false);
+	test_one_map(skel->maps.array_2, skel->progs.read_array_2, true);
+
+	test_pe_preserve_elems__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
new file mode 100644
index 0000000000000..dc77e406de41f
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(int));
+	__uint(value_size, sizeof(int));
+} array_1 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(int));
+	__uint(value_size, sizeof(int));
+	__uint(map_flags, BPF_F_PRESERVE_ELEMS);
+} array_2 SEC(".maps");
+
+SEC("raw_tp/sched_switch")
+int BPF_PROG(read_array_1)
+{
+	struct bpf_perf_event_value val;
+	long ret;
+
+	ret = bpf_perf_event_read_value(&array_1, 0, &val, sizeof(val));
+	bpf_printk("read_array_1 returns %ld", ret);
+	return ret;
+}
+
+SEC("raw_tp/task_rename")
+int BPF_PROG(read_array_2)
+{
+	struct bpf_perf_event_value val;
+	long ret;
+
+	ret = bpf_perf_event_read_value(&array_2, 0, &val, sizeof(val));
+	bpf_printk("read_array_2 returns %ld", ret);
+	return ret;
+}
+
+char LICENSE[] SEC("license") = "GPL";
-- 
2.24.1

Re: [PATCH v3 bpf-next 2/2] selftests/bpf: add tests for BPF_F_PRESERVE_ELEMS

[Alexei Starovoitov]

On Wed, Sep 30, 2020 at 08:20:58AM -0700, Song Liu wrote:
> diff --git a/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
> new file mode 100644
> index 0000000000000..dc77e406de41f
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
> @@ -0,0 +1,44 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2020 Facebook
> +#include "vmlinux.h"

Does it actually need vmlinux.h ?
Just checking to make sure it compiles on older kernels.

> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(int));
> +	__uint(value_size, sizeof(int));
> +} array_1 SEC(".maps");
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(int));
> +	__uint(value_size, sizeof(int));
> +	__uint(map_flags, BPF_F_PRESERVE_ELEMS);
> +} array_2 SEC(".maps");
> +
> +SEC("raw_tp/sched_switch")
> +int BPF_PROG(read_array_1)
> +{
> +	struct bpf_perf_event_value val;
> +	long ret;
> +
> +	ret = bpf_perf_event_read_value(&array_1, 0, &val, sizeof(val));
> +	bpf_printk("read_array_1 returns %ld", ret);
> +	return ret;
> +}
> +
> +SEC("raw_tp/task_rename")
> +int BPF_PROG(read_array_2)
> +{
> +	struct bpf_perf_event_value val;
> +	long ret;
> +
> +	ret = bpf_perf_event_read_value(&array_2, 0, &val, sizeof(val));
> +	bpf_printk("read_array_2 returns %ld", ret);

Please remove printk from the tests. It only spams the trace_pipe.

> +	return ret;

The return code is already checked as far as I can see.
That's enough to pass/fail the test, right?

Re: [PATCH v3 bpf-next 2/2] selftests/bpf: add tests for BPF_F_PRESERVE_ELEMS

[Song Liu]

> On Sep 30, 2020, at 12:26 PM, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> 
> On Wed, Sep 30, 2020 at 08:20:58AM -0700, Song Liu wrote:
>> diff --git a/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
>> new file mode 100644
>> index 0000000000000..dc77e406de41f
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
>> @@ -0,0 +1,44 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +// Copyright (c) 2020 Facebook
>> +#include "vmlinux.h"
> 
> Does it actually need vmlinux.h ?
> Just checking to make sure it compiles on older kernels.

We can include linux/bpf.h instead. 

[...]

>> +	long ret;
>> +
>> +	ret = bpf_perf_event_read_value(&array_2, 0, &val, sizeof(val));
>> +	bpf_printk("read_array_2 returns %ld", ret);
> 
> Please remove printk from the tests. It only spams the trace_pipe.
> 
>> +	return ret;
> 
> The return code is already checked as far as I can see.
> That's enough to pass/fail the test, right?

Yes, we can remove the bpf_printk() here. Fixing this in v4.

Thanks,
Song