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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749534789; bh=33Y0UGYbvh2zMrvnTTnRtLl/ElBvVlGu21fmhR2LOoQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=q+yXadYRl5O/LAR7dkWzypnsu7o3/UHLJd3PFStTq3r4uJTefQl21tG0C/ZqAVz61 bLwTI/AhiMYtVdwxr+SDjax6mzPJ53L7yWGfwSRbLcLq7fBhaPK9fyxVwSSDMaFwE1 tPJOWq7t9Rw3edmi2gg0AGvjaSy5Ars/TEsdVKSpiMPyNfRa1qbNSEEAqwm0/JnTTC Bd1HifpxKolNbqjFUQVFb8kxmY8R1kUrlWCfiN12QC4CQAvn7l/mqTiOL5ADt/JLco V69bhMA4MpZsp43x7XAYyBahnE4qB5kHc815aYTzkJOqz/rjj5feTdYA0fCbHdNoYZ glzdQ94ySkfmQ== Date: Tue, 10 Jun 2025 14:53:05 +0900 From: Masami Hiramatsu (Google) To: Steven Rostedt Cc: LKML , Linux Trace Kernel , Mathieu Desnoyers , Masami Hiramatsu , Mark Rutland , Andrew Morton , Lorenzo Stoakes , Caleb Sander Mateos , Peter Zijlstra , Ingo Molnar , Borislav Petkov , Thomas Gleixner , linux-mm@kvack.org Subject: Re: [RFC][PATCH] tracepoints: Add verifier that makes sure all defined tracepoints are used Message-Id: <20250610145305.c925856f0201fb748c08b331@kernel.org> In-Reply-To: <20250529130138.544ffec4@gandalf.local.home> References: <20250529130138.544ffec4@gandalf.local.home> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 43412100009 X-Stat-Signature: 47pp7mijrxn45m6m17cqsek7kp5y1ts7 X-Rspam-User: X-HE-Tag: 1749534790-234515 X-HE-Meta: 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 hs0zxK10 0ei7CJ8gsgupmJyz+wAiA7nPIpjuZGFhcOm4FSxHgdvYyqne6J/KjXJApCQ0Ql+m116TbWCHmEaAIkkC/8DKrWvW3q/jjMSler19tlYlxGxGjbvNQHQTDe0fwkvIFZJJrMsQgxYqz2fkUePMmqwLGiJsBYrQUOB8L8YmKrYJykPQFm/ugRJ7f/GWaHYetGTqIQPiLYw0G+vlIe5/ssDFokmbcKQr1vcZeE3nNFRvlUzPu1I+sx//Hd15I3v3JM/13CHPsMiCPiTXWZ8f28PtLIVlDdvpu339knt0MrfQEnyCl1z3Gs2Zvwp5YCIQdXaPmMOMuo7aFCb/WdTQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 29 May 2025 13:01:38 -0400 Steven Rostedt wrote: > From: Steven Rostedt > > If a tracepoint is defined via DECLARE_TRACE() or TRACE_EVENT() but never > called (via the trace_() function), its meta data is still > around in memory and not discarded. > > When created via TRACE_EVENT() the situation is worse because the > TRACE_EVENT() creates meta data that can be around 5k per trace event. > Having unused trace events causes several thousand of wasted bytes. > > Add a verifier that injects a pointer to the tracepoint structure in the > functions that are used and added to a section called __tracepoint_check. > Then on boot up, iterate over this section and for every tracepoint > descriptor that is pointed to, update its ".funcs" field to (void *)1, as > the .funcs field is only set when a tracepoint is registered. At this > time, no tracepoints should be registered. > > Then iterate all tracepoints and if any tracepoints doesn't have its > .funcs field set to (void*)1, trigger a warning, and list all tracepoints > that are not found. > > Enabling this currently with a given config produces: > > Tracepoint x86_fpu_before_restore unused > Tracepoint x86_fpu_after_restore unused > Tracepoint x86_fpu_init_state unused > Tracepoint pelt_hw_tp unused > Tracepoint pelt_irq_tp unused > Tracepoint ipi_raise unused > Tracepoint ipi_entry unused > Tracepoint ipi_exit unused > Tracepoint irq_matrix_alloc_reserved unused > Tracepoint psci_domain_idle_enter unused > Tracepoint psci_domain_idle_exit unused > Tracepoint powernv_throttle unused > Tracepoint clock_enable unused > Tracepoint clock_disable unused > Tracepoint clock_set_rate unused > Tracepoint power_domain_target unused > Tracepoint xdp_bulk_tx unused > Tracepoint xdp_redirect_map unused > Tracepoint xdp_redirect_map_err unused > Tracepoint mem_return_failed unused > Tracepoint vma_mas_szero unused > Tracepoint vma_store unused > Tracepoint hugepage_set_pmd unused > Tracepoint hugepage_set_pud unused > Tracepoint hugepage_update_pmd unused > Tracepoint hugepage_update_pud unused > Tracepoint dax_pmd_insert_mapping unused > Tracepoint dax_insert_mapping unused > Tracepoint block_rq_remap unused > Tracepoint xhci_dbc_handle_event unused > Tracepoint xhci_dbc_handle_transfer unused > Tracepoint xhci_dbc_gadget_ep_queue unused > Tracepoint xhci_dbc_alloc_request unused > Tracepoint xhci_dbc_free_request unused > Tracepoint xhci_dbc_queue_request unused > Tracepoint xhci_dbc_giveback_request unused > Tracepoint tcp_ao_wrong_maclen unused > Tracepoint tcp_ao_mismatch unused > Tracepoint tcp_ao_key_not_found unused > Tracepoint tcp_ao_rnext_request unused > Tracepoint tcp_ao_synack_no_key unused > Tracepoint tcp_ao_snd_sne_update unused > Tracepoint tcp_ao_rcv_sne_update unused > > Some of the above is totally unused but others are not used due to their > "trace_" functions being inside configs, in which case, the defined > tracepoints should also be inside those same configs. Others are > architecture specific but defined in generic code, where they should > either be moved to the architecture or be surrounded by #ifdef for the > architectures they are for. > > Note, currently this only handles tracepoints that are builtin. This can > easily be extended to verify tracepoints used by modules, but it requires a > slightly different approach as it needs updates to the module code. > > Link: https://lore.kernel.org/all/20250528114549.4d8a5e03@gandalf.local.home/ > > Signed-off-by: Steven Rostedt (Google) > --- > include/asm-generic/vmlinux.lds.h | 1 + > include/linux/tracepoint.h | 10 ++++++++++ > kernel/trace/Kconfig | 8 ++++++++ > kernel/tracepoint.c | 26 ++++++++++++++++++++++++++ > 4 files changed, 45 insertions(+) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index fa5f19b8d53a..600d8b51e315 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -708,6 +708,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) > MCOUNT_REC() \ > *(.init.rodata .init.rodata.*) \ > FTRACE_EVENTS() \ > + BOUNDED_SECTION_BY(__tracepoint_check, ___tracepoint_check) \ nit: Shouldn't we also make this as TRACEPOINT_CHECKS() ? Others looks good to me. Reviewed-by: Masami Hiramatsu (Google) Thank you, > TRACE_SYSCALLS() \ > KPROBE_BLACKLIST() \ > ERROR_INJECT_WHITELIST() \ > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > index a351763e6965..c9c03ec8e552 100644 > --- a/include/linux/tracepoint.h > +++ b/include/linux/tracepoint.h > @@ -221,6 +221,14 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > __do_trace_##name(args); \ > } > > +#ifdef CONFIG_TRACEPOINT_VERIFY_USED > +# define TRACEPOINT_CHECK(name) \ > + static void __used __section("__tracepoint_check") *__trace_check = \ > + &__tracepoint_##name; > +#else > +# define TRACEPOINT_CHECK(name) > +#endif > + > /* > * Make sure the alignment of the structure in the __tracepoints section will > * not add unwanted padding between the beginning of the section and the > @@ -270,6 +278,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > __DECLARE_TRACE_COMMON(name, PARAMS(proto), PARAMS(args), PARAMS(data_proto)) \ > static inline void __do_trace_##name(proto) \ > { \ > + TRACEPOINT_CHECK(name) \ > if (cond) { \ > guard(preempt_notrace)(); \ > __DO_TRACE_CALL(name, TP_ARGS(args)); \ > @@ -289,6 +298,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > __DECLARE_TRACE_COMMON(name, PARAMS(proto), PARAMS(args), PARAMS(data_proto)) \ > static inline void __do_trace_##name(proto) \ > { \ > + TRACEPOINT_CHECK(name) \ > guard(rcu_tasks_trace)(); \ > __DO_TRACE_CALL(name, TP_ARGS(args)); \ > } \ > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > index a3f35c7d83b6..8867eee5b58f 100644 > --- a/kernel/trace/Kconfig > +++ b/kernel/trace/Kconfig > @@ -1044,6 +1044,14 @@ config GCOV_PROFILE_FTRACE > Note that on a kernel compiled with this config, ftrace will > run significantly slower. > > +config TRACEPOINT_VERIFY_USED > + bool "Verify that all defined tracepoints are used" > + depends on TRACEPOINTS > + help > + This option checks if every builtin defined tracepoint is > + used in the code. If a tracepoint is defined but not used, > + it will waste memory as its meta data is still created. > + > config FTRACE_SELFTEST > bool > > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c > index 62719d2941c9..f354d3850a04 100644 > --- a/kernel/tracepoint.c > +++ b/kernel/tracepoint.c > @@ -677,10 +677,36 @@ static struct notifier_block tracepoint_module_nb = { > .priority = 0, > }; > > +#ifdef CONFIG_TRACEPOINT_VERIFY_USED > +extern void * __start___tracepoint_check[]; > +extern void * __stop___tracepoint_check[]; > + > +#define VERIFIED_TRACEPOINT ((void *)1) > + > +static void check_tracepoint(struct tracepoint *tp, void *priv) > +{ > + if (WARN_ONCE(tp->funcs != VERIFIED_TRACEPOINT, "Unused tracepoints found")) > + pr_warn("Tracepoint %s unused\n", tp->name); > + > + tp->funcs = NULL; > +} > +#endif > + > static __init int init_tracepoints(void) > { > int ret; > > +#ifdef CONFIG_TRACEPOINT_VERIFY_USED > + for (void **ptr = __start___tracepoint_check; > + ptr < __stop___tracepoint_check; ptr++) { > + struct tracepoint *tp = *ptr; > + > + tp->funcs = VERIFIED_TRACEPOINT; > + } > + > + for_each_kernel_tracepoint(check_tracepoint, NULL); > +#endif > + > ret = register_module_notifier(&tracepoint_module_nb); > if (ret) > pr_warn("Failed to register tracepoint module enter notifier\n"); > -- > 2.47.2 > -- Masami Hiramatsu (Google)