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Wed, 14 Jan 2026 13:06:17 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 14 Jan 2026 22:06:16 +0100 To: Alan Maguire Cc: Tao Chen , Alexei Starovoitov , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , LKML , bpf Subject: Re: The same symbol is printed twice when use tracepoint to get stack Message-ID: References: <31e5d219-07f4-46c0-bef1-53af20d473f1@oracle.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <31e5d219-07f4-46c0-bef1-53af20d473f1@oracle.com> 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; > > } > > >