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

[Tao Chen]

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@xxxxxxxxxx/
>
> > Alan
> >
> > [1] https://lore.kernel.org/bpf/20251104215405.168643-2-jolsa@xxxxxxxxxx/
> > [2] https://lore.kernel.org/all/a38fed68-67bc-98ce-8e12-743342121ae3@xxxxxxxxxx/
> >   
> > > 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