linux-kernel - The same symbol is printed twice when use tracepoint to get stack

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Message-ID: <e876fdea-ad0c-49dd-80ec-bd835ebfe0a4@linux.dev>
Date: Wed, 14 Jan 2026 23:09:21 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>, Jiri Olsa <jolsa@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: The same symbol is printed twice when use tracepoint to get stack

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