On Thu, 29 May 2025 13:01:38 -0400 Steven Rostedt <rost...@goodmis.org> wrote:
> From: Steven Rostedt <rost...@goodmis.org> > > If a tracepoint is defined via DECLARE_TRACE() or TRACE_EVENT() but never > called (via the trace_<tracepoint>() 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/20250528114549.4d8a5...@gandalf.local.home/ > > Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org> > --- > 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) <mhira...@kernel.org> 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) <mhira...@kernel.org>
