Re: The same symbol is printed twice when use tracepoint to get stack

[Tao Chen <chen.dylane@linux.dev>]

在 2026/1/15 05:06, Jiri Olsa 写道:
> On Wed, Jan 14, 2026 at 05:35:45PM +0000, Alan Maguire wrote:
>> On 14/01/2026 15:09, Tao Chen wrote:
>>> 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.
>>>
>>
>> You may need the fix Jiri provided for x86_64 [1]. Eugene mentioned that
>> the issue persists for arm64 however [2].
> 
> yep, there's also follow patchset up for kprobe multi [1]
> 
> jirka
> 
> 
> [1] https://lore.kernel.org/bpf/20260112214940.1222115-1-jolsa@kernel.org/
> 
>>
>> Alan
>>
>> [1] https://lore.kernel.org/bpf/20251104215405.168643-2-jolsa@kernel.org/
>> [2] https://lore.kernel.org/all/a38fed68-67bc-98ce-8e12-743342121ae3@oracle.com/
>>   
>>> 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;
>>> }
>>>
>>

Alan, Jiri

Thanks for your reply, i see.

-- 
Best Regards
Tao Chen