On 6/24/20 1:37 PM, Song Liu wrote:
On Jun 23, 2020, at 3:27 PM, Yonghong Song <yhs@xxxxxx> wrote:
On 6/23/20 3:07 PM, Song Liu wrote:
On Jun 23, 2020, at 11:57 AM, Yonghong Song <yhs@xxxxxx> wrote:
On 6/23/20 12:08 AM, Song Liu wrote:
The new test is similar to other bpf_iter tests.
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
.../selftests/bpf/prog_tests/bpf_iter.c | 17 +++++++
.../selftests/bpf/progs/bpf_iter_task_stack.c | 50 +++++++++++++++++++
2 files changed, 67 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 87c29dde1cf96..baa83328f810d 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -5,6 +5,7 @@
#include "bpf_iter_netlink.skel.h"
#include "bpf_iter_bpf_map.skel.h"
#include "bpf_iter_task.skel.h"
+#include "bpf_iter_task_stack.skel.h"
#include "bpf_iter_task_file.skel.h"
#include "bpf_iter_test_kern1.skel.h"
#include "bpf_iter_test_kern2.skel.h"
@@ -106,6 +107,20 @@ static void test_task(void)
bpf_iter_task__destroy(skel);
}
+static void test_task_stack(void)
+{
+ struct bpf_iter_task_stack *skel;
+
+ skel = bpf_iter_task_stack__open_and_load();
+ if (CHECK(!skel, "bpf_iter_task_stack__open_and_load",
+ "skeleton open_and_load failed\n"))
+ return;
+
+ do_dummy_read(skel->progs.dump_task_stack);
+
+ bpf_iter_task_stack__destroy(skel);
+}
+
static void test_task_file(void)
{
struct bpf_iter_task_file *skel;
@@ -392,6 +407,8 @@ void test_bpf_iter(void)
test_bpf_map();
if (test__start_subtest("task"))
test_task();
+ if (test__start_subtest("task_stack"))
+ test_task_stack();
if (test__start_subtest("task_file"))
test_task_file();
if (test__start_subtest("anon"))
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
new file mode 100644
index 0000000000000..4fc939e0fca77
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__task bpf_iter__task___not_used
+#include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__task
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct bpf_iter_meta {
+ struct seq_file *seq;
+ __u64 session_id;
+ __u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__task {
+ struct bpf_iter_meta *meta;
+ struct task_struct *task;
+} __attribute__((preserve_access_index));
+
+#define MAX_STACK_TRACE_DEPTH 64
+unsigned long entries[MAX_STACK_TRACE_DEPTH];
+
+SEC("iter/task")
+int dump_task_stack(struct bpf_iter__task *ctx)
+{
+ struct seq_file *seq = ctx->meta->seq;
+ struct task_struct *task = ctx->task;
+ unsigned int i, num_entries;
+
+ if (task == (void *)0)
+ return 0;
+
+ num_entries = bpf_get_task_stack_trace(task, entries, MAX_STACK_TRACE_DEPTH);
+
+ BPF_SEQ_PRINTF(seq, "pid: %8u\n", task->pid);
+
+ for (i = 0; i < MAX_STACK_TRACE_DEPTH; i++) {
+ if (num_entries > i)
+ BPF_SEQ_PRINTF(seq, "[<0>] %pB\n", (void *)entries[i]);
We may have an issue on 32bit issue.
On 32bit system, the following is called in the kernel
+ return stack_trace_save_tsk(task, (unsigned long *)entries, size, 0);
it will pack addresses at 4 byte increment.
But in BPF program, the reading is in 8 byte increment.
Can we avoid potential issues by requiring size % 8 == 0? Or maybe round down
size to closest multiple of 8?
This is what I mean:
for bpf program: "long" means u64, so we allocate 64 * 8 buffer size
and pass it to the helper
in the helper, the address will be increased along sizeof(long), which
is 4 for 32bit system.
So address is recorded at buf, buf + 4, buf + 8, buf + 12, ...
After the helper returns, the bpf program tries to retrieve
the address at buf, buf + 8, buf + 16.
The helper itself is okay. But BPF_SEQ_PRINTF above is wrong.
Is this interpretation correct?
Thanks for the clarification. I guess the best solution is to fix this
once in the kernel, so BPF programs don't have to worry about it.
The kernel could make each entry 8 bytes. This will cause less potential
entries for 32bit, probably fine. Another option is BPF program declares
an extern variable CONFIG_64BIT and it is 'y', that means 64 bit.
Otherwise it is 32bit. libbpf should set CONFIG_64BIT correctly.
I guess storing each address as 64bit probably a better and less
confusion choice.
Song
