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

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Message-ID: <aWgFSJIpsP2M6mYA@krava>
Date: Wed, 14 Jan 2026 22:06:16 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Alan Maguire <alan.maguire@...cle.com>
Cc: Tao Chen <chen.dylane@...ux.dev>, 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>,
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: The same symbol is printed twice when use tracepoint to get stack

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;
> > }
> > 
>