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Mon, 22 Dec 2025 01:27:47 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 22 Dec 2025 10:27:40 +0100 To: Steven Rostedt Cc: LKML , Linux Trace Kernel , Masami Hiramatsu , Mathieu Desnoyers , Ian Rogers , Arnaldo Carvalho de Melo , Namhyung Kim Subject: Re: [PATCH] tracing: Do not register unsupported perf events Message-ID: References: <20251216182440.147e4453@gandalf.local.home> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251216182440.147e4453@gandalf.local.home> On Tue, Dec 16, 2025 at 06:24:40PM -0500, Steven Rostedt wrote: > From: Steven Rostedt > > Synthetic events currently do not have a function to register perf events. > This leads to calling the tracepoint register functions with a NULL > function pointer which triggers: > > ------------[ cut here ]------------ > WARNING: kernel/tracepoint.c:175 at tracepoint_add_func+0x357/0x370, CPU#2: perf/2272 > Modules linked in: kvm_intel kvm irqbypass > CPU: 2 UID: 0 PID: 2272 Comm: perf Not tainted 6.18.0-ftest-11964-ge022764176fc-dirty #323 PREEMPTLAZY > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 > RIP: 0010:tracepoint_add_func+0x357/0x370 > Code: 28 9c e8 4c 0b f5 ff eb 0f 4c 89 f7 48 c7 c6 80 4d 28 9c e8 ab 89 f4 ff 31 c0 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc <0f> 0b 49 c7 c6 ea ff ff ff e9 ee fe ff ff 0f 0b e9 f9 fe ff ff 0f > RSP: 0018:ffffabc0c44d3c40 EFLAGS: 00010246 > RAX: 0000000000000001 RBX: ffff9380aa9e4060 RCX: 0000000000000000 > RDX: 000000000000000a RSI: ffffffff9e1d4a98 RDI: ffff937fcf5fd6c8 > RBP: 0000000000000001 R08: 0000000000000007 R09: ffff937fcf5fc780 > R10: 0000000000000003 R11: ffffffff9c193910 R12: 000000000000000a > R13: ffffffff9e1e5888 R14: 0000000000000000 R15: ffffabc0c44d3c78 > FS: 00007f6202f5f340(0000) GS:ffff93819f00f000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 000055d3162281a8 CR3: 0000000106a56003 CR4: 0000000000172ef0 > Call Trace: > > tracepoint_probe_register+0x5d/0x90 > synth_event_reg+0x3c/0x60 > perf_trace_event_init+0x204/0x340 > perf_trace_init+0x85/0xd0 > perf_tp_event_init+0x2e/0x50 > perf_try_init_event+0x6f/0x230 > ? perf_event_alloc+0x4bb/0xdc0 > perf_event_alloc+0x65a/0xdc0 > __se_sys_perf_event_open+0x290/0x9f0 > do_syscall_64+0x93/0x7b0 > ? entry_SYSCALL_64_after_hwframe+0x76/0x7e > ? trace_hardirqs_off+0x53/0xc0 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > Instead, have the code return -ENODEV, which doesn't warn and has perf > error out with: > > # perf record -e synthetic:futex_wait > Error: > The sys_perf_event_open() syscall returned with 19 (No such device) for event (synthetic:futex_wait). > "dmesg | grep -i perf" may provide additional information. > > Ideally perf should support synthetic events, but for now just fix the > warning. The support can come later. > > Cc: stable@vger.kernel.org > Fixes: 4b147936fa509 ("tracing: Add support for 'synthetic' events") > Reported-by: Ian Rogers > Signed-off-by: Steven Rostedt (Google) lgtm Acked-by: Jiri Olsa jirka > --- > kernel/trace/trace_events.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index a5a93d243047..754b14ca87a7 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -710,6 +710,8 @@ int trace_event_reg(struct trace_event_call *call, > > #ifdef CONFIG_PERF_EVENTS > case TRACE_REG_PERF_REGISTER: > + if (!call->class->perf_probe) > + return -ENODEV; > return tracepoint_probe_register(call->tp, > call->class->perf_probe, > call); > -- > 2.51.0 >