From: Tao Chen <chen.dylane@linux.dev>
To: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
Jiri Olsa <jolsa@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
bpf <bpf@vger.kernel.org>
Subject: The same symbol is printed twice when use tracepoint to get stack
Date: Wed, 14 Jan 2026 23:09:21 +0800 [thread overview]
Message-ID: <e876fdea-ad0c-49dd-80ec-bd835ebfe0a4@linux.dev> (raw)
Hi guys,
When using tracepoints to retrieve stack information, I observed that
perf_trace_sched_migrate_task was printed twice. And the issue also
occurs with tools using libbpf.
sudo bpftrace -e '
tracepoint:sched:sched_migrate_task {
printf("Task %s migrated by:\n", args->comm);
print(kstack);
}'
Task kcompactd0 migrated by:
perf_trace_sched_migrate_task+9
perf_trace_sched_migrate_task+9
set_task_cpu+353
detach_task+77
detach_tasks+281
sched_balance_rq+452
sched_balance_newidle+504
pick_next_task_fair+84
__pick_next_task+66
pick_next_task+43
__schedule+332
schedule+41
schedule_hrtimeout_range+239
do_poll.constprop.0+668
do_sys_poll+499
__x64_sys_ppoll+220
x64_sys_call+5722
do_syscall_64+126
entry_SYSCALL_64_after_hwframe+118
Task jbd2/sda2-8 migrated by:
perf_trace_sched_migrate_task+9
perf_trace_sched_migrate_task+9
set_task_cpu+353
try_to_wake_up+365
default_wake_function+26
autoremove_wake_function+18
__wake_up_common+118
__wake_up+55
__jbd2_log_start_commit+195
env:
bpftrace v0.21.2
ubuntu24.04，6.14.0-36-generic
The issue is as follows:
https://github.com/bpftrace/bpftrace/issues/4949
It seems that there is no special handling in the kernel.
Does anyone has thoughts on this issue. Thanks.
BPF_CALL_4(bpf_get_stack_raw_tp, struct bpf_raw_tracepoint_args *, args,
void *, buf, u32, size, u64, flags)
{
struct pt_regs *regs = get_bpf_raw_tp_regs();
int ret;
if (IS_ERR(regs))
return PTR_ERR(regs);
perf_fetch_caller_regs(regs);
ret = bpf_get_stack((unsigned long) regs, (unsigned long) buf,
(unsigned long) size, flags, 0);
put_bpf_raw_tp_regs();
return ret;
}
--
Best Regards
Tao Chen
next reply other threads:[~2026-01-14 15:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-14 15:09 Tao Chen [this message]
2026-01-14 17:35 ` The same symbol is printed twice when use tracepoint to get stack Alan Maguire
2026-01-14 21:06 ` Jiri Olsa
2026-01-15 2:18 ` Tao Chen
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