This set introduces a new helper bpf_get_task_stack(). The primary use case
is to dump all /proc/*/stack to seq_file via bpf_iter__task.
A few different approaches have been explored and compared:
1. A simple wrapper around stack_trace_save_tsk(), as v1 [1].
This approach introduces new syntax, which is different to existing
helper bpf_get_stack(). Therefore, this is not ideal.
2. Extend get_perf_callchain() to support "task" as argument.
This approach reuses most of bpf_get_stack(). However, extending
get_perf_callchain() requires non-trivial changes to architecture
specific code. Which is error prone.
3. Current (v2) approach, leverages most of existing bpf_get_stack(), and
uses stack_trace_save_tsk() to handle architecture specific logic.
[1] https://lore.kernel.org/netdev/[email protected]/
Changes v2 => v3:
1. Rebase on top of bpf-next. (Yonghong)
2. Sanitize get_callchain_entry(). (Peter)
3. Use has_callchain_buf for bpf_get_task_stack. (Andrii)
4. Other small clean up. (Yonghong, Andrii).
Changes v1 => v2:
1. Reuse most of bpf_get_stack() logic. (Andrii)
2. Fix unsigned long vs. u64 mismatch for 32-bit systems. (Yonghong)
3. Add %pB support in bpf_trace_printk(). (Daniel)
4. Fix buffer size to bytes.
Song Liu (4):
perf: expose get/put_callchain_entry()
bpf: introduce helper bpf_get_task_stack()
bpf: allow %pB in bpf_seq_printf() and bpf_trace_printk()
selftests/bpf: add bpf_iter test with bpf_get_task_stack()
include/linux/bpf.h | 1 +
include/linux/perf_event.h | 2 +
include/uapi/linux/bpf.h | 36 ++++++++-
kernel/bpf/stackmap.c | 75 ++++++++++++++++++-
kernel/bpf/verifier.c | 4 +-
kernel/events/callchain.c | 13 ++--
kernel/trace/bpf_trace.c | 12 ++-
scripts/bpf_helpers_doc.py | 2 +
tools/include/uapi/linux/bpf.h | 36 ++++++++-
.../selftests/bpf/prog_tests/bpf_iter.c | 17 +++++
.../selftests/bpf/progs/bpf_iter_task_stack.c | 53 +++++++++++++
11 files changed, 236 insertions(+), 15 deletions(-)
create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
--
2.24.1
The new test is similar to other bpf_iter tests.
Signed-off-by: Song Liu <[email protected]>
---
.../selftests/bpf/prog_tests/bpf_iter.c | 17 ++++++
.../selftests/bpf/progs/bpf_iter_task_stack.c | 53 +++++++++++++++++++
2 files changed, 70 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 1e2e0fced6e81..fed42755416db 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_tcp4.skel.h"
#include "bpf_iter_tcp6.skel.h"
@@ -110,6 +111,20 @@ 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;
@@ -452,6 +467,8 @@ 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("tcp4"))
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..39b21df17c3ee
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
@@ -0,0 +1,53 @@
+// 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];
+#define SIZE_OF_ULONG (sizeof(unsigned long))
+
+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;
+ long i, retlen;
+
+ if (task == (void *)0)
+ return 0;
+
+ retlen = bpf_get_task_stack(task, entries,
+ MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, 0);
+ if (retlen < 0)
+ return 0;
+
+ BPF_SEQ_PRINTF(seq, "pid: %8u num_entries: %8u\n", task->pid,
+ retlen / SIZE_OF_ULONG);
+ for (i = 0; i < MAX_STACK_TRACE_DEPTH; i++) {
+ if (retlen > i * SIZE_OF_ULONG)
+ BPF_SEQ_PRINTF(seq, "[<0>] %pB\n", (void *)entries[i]);
+ }
+ BPF_SEQ_PRINTF(seq, "\n");
+
+ return 0;
+}
--
2.24.1
Introduce helper bpf_get_task_stack(), which dumps stack trace of given
task. This is different to bpf_get_stack(), which gets stack track of
current task. One potential use case of bpf_get_task_stack() is to call
it from bpf_iter__task and dump all /proc/<pid>/stack to a seq_file.
bpf_get_task_stack() uses stack_trace_save_tsk() instead of
get_perf_callchain() for kernel stack. The benefit of this choice is that
stack_trace_save_tsk() doesn't require changes in arch/. The downside of
using stack_trace_save_tsk() is that stack_trace_save_tsk() dumps the
stack trace to unsigned long array. For 32-bit systems, we need to
translate it to u64 array.
Acked-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Song Liu <[email protected]>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 36 +++++++++++++++-
kernel/bpf/stackmap.c | 75 ++++++++++++++++++++++++++++++++--
kernel/bpf/verifier.c | 4 +-
kernel/trace/bpf_trace.c | 2 +
scripts/bpf_helpers_doc.py | 2 +
tools/include/uapi/linux/bpf.h | 36 +++++++++++++++-
7 files changed, 150 insertions(+), 6 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 3d2ade703a357..0cd7f6884c5cd 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1627,6 +1627,7 @@ extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;
extern const struct bpf_func_proto bpf_get_current_comm_proto;
extern const struct bpf_func_proto bpf_get_stackid_proto;
extern const struct bpf_func_proto bpf_get_stack_proto;
+extern const struct bpf_func_proto bpf_get_task_stack_proto;
extern const struct bpf_func_proto bpf_sock_map_update_proto;
extern const struct bpf_func_proto bpf_sock_hash_update_proto;
extern const struct bpf_func_proto bpf_get_current_cgroup_id_proto;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0cb8ec9488168..54106ea667211 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3285,6 +3285,39 @@ union bpf_attr {
* Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
* Return
* *sk* if casting is valid, or NULL otherwise.
+ *
+ * long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags)
+ * Description
+ * Return a user or a kernel stack in bpf program provided buffer.
+ * To achieve this, the helper needs *task*, which is a valid
+ * pointer to struct task_struct. To store the stacktrace, the
+ * bpf program provides *buf* with a nonnegative *size*.
+ *
+ * The last argument, *flags*, holds the number of stack frames to
+ * skip (from 0 to 255), masked with
+ * **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
+ * the following flags:
+ *
+ * **BPF_F_USER_STACK**
+ * Collect a user space stack instead of a kernel stack.
+ * **BPF_F_USER_BUILD_ID**
+ * Collect buildid+offset instead of ips for user stack,
+ * only valid if **BPF_F_USER_STACK** is also specified.
+ *
+ * **bpf_get_task_stack**\ () can collect up to
+ * **PERF_MAX_STACK_DEPTH** both kernel and user frames, subject
+ * to sufficient large buffer size. Note that
+ * this limit can be controlled with the **sysctl** program, and
+ * that it should be manually increased in order to profile long
+ * user stacks (such as stacks for Java programs). To do so, use:
+ *
+ * ::
+ *
+ * # sysctl kernel.perf_event_max_stack=<new value>
+ * Return
+ * A non-negative value equal to or less than *size* on success,
+ * or a negative error in case of failure.
+ *
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3427,7 +3460,8 @@ union bpf_attr {
FN(skc_to_tcp_sock), \
FN(skc_to_tcp_timewait_sock), \
FN(skc_to_tcp_request_sock), \
- FN(skc_to_udp6_sock),
+ FN(skc_to_udp6_sock), \
+ FN(get_task_stack),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 27dc9b1b08a52..0ba66b29ef227 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -348,6 +348,40 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
}
}
+static struct perf_callchain_entry *
+get_callchain_entry_for_task(struct task_struct *task, u32 init_nr)
+{
+ struct perf_callchain_entry *entry;
+ int rctx;
+
+ entry = get_callchain_entry(&rctx);
+
+ if (!entry)
+ return NULL;
+
+ entry->nr = init_nr +
+ stack_trace_save_tsk(task, (unsigned long *)(entry->ip + init_nr),
+ sysctl_perf_event_max_stack - init_nr, 0);
+
+ /* stack_trace_save_tsk() works on unsigned long array, while
+ * perf_callchain_entry uses u64 array. For 32-bit systems, it is
+ * necessary to fix this mismatch.
+ */
+ if (__BITS_PER_LONG != 64) {
+ unsigned long *from = (unsigned long *) entry->ip;
+ u64 *to = entry->ip;
+ int i;
+
+ /* copy data from the end to avoid using extra buffer */
+ for (i = entry->nr - 1; i >= (int)init_nr; i--)
+ to[i] = (u64)(from[i]);
+ }
+
+ put_callchain_entry(rctx);
+
+ return entry;
+}
+
BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
u64, flags)
{
@@ -448,8 +482,8 @@ const struct bpf_func_proto bpf_get_stackid_proto = {
.arg3_type = ARG_ANYTHING,
};
-BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
- u64, flags)
+static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
+ void *buf, u32 size, u64 flags)
{
u32 init_nr, trace_nr, copy_len, elem_size, num_elem;
bool user_build_id = flags & BPF_F_USER_BUILD_ID;
@@ -471,13 +505,22 @@ BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
if (unlikely(size % elem_size))
goto clear;
+ /* cannot get valid user stack for task without user_mode regs */
+ if (task && user && !user_mode(regs))
+ goto err_fault;
+
num_elem = size / elem_size;
if (sysctl_perf_event_max_stack < num_elem)
init_nr = 0;
else
init_nr = sysctl_perf_event_max_stack - num_elem;
+
+ if (kernel && task)
+ trace = get_callchain_entry_for_task(task, init_nr);
+ else
trace = get_perf_callchain(regs, init_nr, kernel, user,
- sysctl_perf_event_max_stack, false, false);
+ sysctl_perf_event_max_stack,
+ false, false);
if (unlikely(!trace))
goto err_fault;
@@ -505,6 +548,12 @@ BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
return err;
}
+BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
+ u64, flags)
+{
+ return __bpf_get_stack(regs, NULL, buf, size, flags);
+}
+
const struct bpf_func_proto bpf_get_stack_proto = {
.func = bpf_get_stack,
.gpl_only = true,
@@ -515,6 +564,26 @@ const struct bpf_func_proto bpf_get_stack_proto = {
.arg4_type = ARG_ANYTHING,
};
+BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf,
+ u32, size, u64, flags)
+{
+ struct pt_regs *regs = task_pt_regs(task);
+
+ return __bpf_get_stack(regs, task, buf, size, flags);
+}
+
+static int bpf_get_task_stack_btf_ids[5];
+const struct bpf_func_proto bpf_get_task_stack_proto = {
+ .func = bpf_get_task_stack,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg2_type = ARG_PTR_TO_UNINIT_MEM,
+ .arg3_type = ARG_CONST_SIZE_OR_ZERO,
+ .arg4_type = ARG_ANYTHING,
+ .btf_id = bpf_get_task_stack_btf_ids,
+};
+
/* Called from eBPF program */
static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
{
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7de98906ddf4a..b608185e1ffd5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4864,7 +4864,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
if (err)
return err;
- if (func_id == BPF_FUNC_get_stack && !env->prog->has_callchain_buf) {
+ if ((func_id == BPF_FUNC_get_stack ||
+ func_id == BPF_FUNC_get_task_stack) &&
+ !env->prog->has_callchain_buf) {
const char *err_str;
#ifdef CONFIG_PERF_EVENTS
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 5d59dda5f6615..977ba3b6f6c64 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1137,6 +1137,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_ringbuf_query_proto;
case BPF_FUNC_jiffies64:
return &bpf_jiffies64_proto;
+ case BPF_FUNC_get_task_stack:
+ return &bpf_get_task_stack_proto;
default:
return NULL;
}
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index 6bab40ff442e8..dd12e3b18aae3 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -426,6 +426,7 @@ class PrinterHelpers(Printer):
'struct tcp_timewait_sock',
'struct tcp_request_sock',
'struct udp6_sock',
+ 'struct task_struct',
'struct __sk_buff',
'struct sk_msg_md',
@@ -468,6 +469,7 @@ class PrinterHelpers(Printer):
'struct tcp_timewait_sock',
'struct tcp_request_sock',
'struct udp6_sock',
+ 'struct task_struct',
}
mapped_types = {
'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 0cb8ec9488168..54106ea667211 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3285,6 +3285,39 @@ union bpf_attr {
* Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
* Return
* *sk* if casting is valid, or NULL otherwise.
+ *
+ * long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags)
+ * Description
+ * Return a user or a kernel stack in bpf program provided buffer.
+ * To achieve this, the helper needs *task*, which is a valid
+ * pointer to struct task_struct. To store the stacktrace, the
+ * bpf program provides *buf* with a nonnegative *size*.
+ *
+ * The last argument, *flags*, holds the number of stack frames to
+ * skip (from 0 to 255), masked with
+ * **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
+ * the following flags:
+ *
+ * **BPF_F_USER_STACK**
+ * Collect a user space stack instead of a kernel stack.
+ * **BPF_F_USER_BUILD_ID**
+ * Collect buildid+offset instead of ips for user stack,
+ * only valid if **BPF_F_USER_STACK** is also specified.
+ *
+ * **bpf_get_task_stack**\ () can collect up to
+ * **PERF_MAX_STACK_DEPTH** both kernel and user frames, subject
+ * to sufficient large buffer size. Note that
+ * this limit can be controlled with the **sysctl** program, and
+ * that it should be manually increased in order to profile long
+ * user stacks (such as stacks for Java programs). To do so, use:
+ *
+ * ::
+ *
+ * # sysctl kernel.perf_event_max_stack=<new value>
+ * Return
+ * A non-negative value equal to or less than *size* on success,
+ * or a negative error in case of failure.
+ *
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3427,7 +3460,8 @@ union bpf_attr {
FN(skc_to_tcp_sock), \
FN(skc_to_tcp_timewait_sock), \
FN(skc_to_tcp_request_sock), \
- FN(skc_to_udp6_sock),
+ FN(skc_to_udp6_sock), \
+ FN(get_task_stack),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
--
2.24.1
This makes it easy to dump stack trace in text.
Acked-by: Yonghong Song <[email protected]>
Signed-off-by: Song Liu <[email protected]>
---
kernel/trace/bpf_trace.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 977ba3b6f6c64..1d874d8e4384b 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -376,7 +376,7 @@ static void bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
/*
* Only limited trace_printk() conversion specifiers allowed:
- * %d %i %u %x %ld %li %lu %lx %lld %lli %llu %llx %p %pks %pus %s
+ * %d %i %u %x %ld %li %lu %lx %lld %lli %llu %llx %p %pB %pks %pus %s
*/
BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
u64, arg2, u64, arg3)
@@ -420,6 +420,11 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
goto fmt_str;
}
+ if (fmt[i + 1] == 'B') {
+ i++;
+ goto fmt_next;
+ }
+
/* disallow any further format extensions */
if (fmt[i + 1] != 0 &&
!isspace(fmt[i + 1]) &&
@@ -636,7 +641,8 @@ BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
if (fmt[i] == 'p') {
if (fmt[i + 1] == 0 ||
fmt[i + 1] == 'K' ||
- fmt[i + 1] == 'x') {
+ fmt[i + 1] == 'x' ||
+ fmt[i + 1] == 'B') {
/* just kernel pointers */
params[fmt_cnt] = args[fmt_cnt];
fmt_cnt++;
--
2.24.1
On 6/26/20 5:26 PM, Song Liu wrote:
> The new test is similar to other bpf_iter tests.
It would be great if you can show some results from
bpf_iter_task_stack.c dump.
>
> Signed-off-by: Song Liu <[email protected]>
> ---
> .../selftests/bpf/prog_tests/bpf_iter.c | 17 ++++++
> .../selftests/bpf/progs/bpf_iter_task_stack.c | 53 +++++++++++++++++++
> 2 files changed, 70 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 1e2e0fced6e81..fed42755416db 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_tcp4.skel.h"
> #include "bpf_iter_tcp6.skel.h"
> @@ -110,6 +111,20 @@ 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;
> @@ -452,6 +467,8 @@ 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("tcp4"))
> 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..39b21df17c3ee
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
> @@ -0,0 +1,53 @@
> +// 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));
Please take a look at bpf_iter_task.c. The above code can be simplified as
#include "bpf_iter.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
> +
> +#define MAX_STACK_TRACE_DEPTH 64
> +unsigned long entries[MAX_STACK_TRACE_DEPTH];
> +#define SIZE_OF_ULONG (sizeof(unsigned long))
> +
> +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;
> + long i, retlen;
> +
> + if (task == (void *)0)
> + return 0;
> +
> + retlen = bpf_get_task_stack(task, entries,
> + MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, 0);
> + if (retlen < 0)
> + return 0;
> +
> + BPF_SEQ_PRINTF(seq, "pid: %8u num_entries: %8u\n", task->pid,
> + retlen / SIZE_OF_ULONG);
> + for (i = 0; i < MAX_STACK_TRACE_DEPTH; i++) {
> + if (retlen > i * SIZE_OF_ULONG)
> + BPF_SEQ_PRINTF(seq, "[<0>] %pB\n", (void *)entries[i]);
> + }
> + BPF_SEQ_PRINTF(seq, "\n");
> +
> + return 0;
> +}
>
On Fri, Jun 26, 2020 at 5:29 PM Song Liu <[email protected]> wrote:
>
> Introduce helper bpf_get_task_stack(), which dumps stack trace of given
> task. This is different to bpf_get_stack(), which gets stack track of
> current task. One potential use case of bpf_get_task_stack() is to call
> it from bpf_iter__task and dump all /proc/<pid>/stack to a seq_file.
>
> bpf_get_task_stack() uses stack_trace_save_tsk() instead of
> get_perf_callchain() for kernel stack. The benefit of this choice is that
> stack_trace_save_tsk() doesn't require changes in arch/. The downside of
> using stack_trace_save_tsk() is that stack_trace_save_tsk() dumps the
> stack trace to unsigned long array. For 32-bit systems, we need to
> translate it to u64 array.
>
> Acked-by: Andrii Nakryiko <[email protected]>
> Signed-off-by: Song Liu <[email protected]>
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 36 +++++++++++++++-
> kernel/bpf/stackmap.c | 75 ++++++++++++++++++++++++++++++++--
> kernel/bpf/verifier.c | 4 +-
> kernel/trace/bpf_trace.c | 2 +
> scripts/bpf_helpers_doc.py | 2 +
> tools/include/uapi/linux/bpf.h | 36 +++++++++++++++-
> 7 files changed, 150 insertions(+), 6 deletions(-)
>
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 7de98906ddf4a..b608185e1ffd5 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4864,7 +4864,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
> if (err)
> return err;
>
> - if (func_id == BPF_FUNC_get_stack && !env->prog->has_callchain_buf) {
> + if ((func_id == BPF_FUNC_get_stack ||
> + func_id == BPF_FUNC_get_task_stack) &&
> + !env->prog->has_callchain_buf) {
> const char *err_str;
>
I'm glad it was so simple :) Thanks for checking!
[...]