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Message-ID: <ZIbr5Ou1Q1Aqf2vg@FVFF77S0Q05N>
Date: Mon, 12 Jun 2023 10:56:52 +0100
From: Mark Rutland <mark.rutland@....com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Kees Cook <keescook@...omium.org>,
Miguel Ojeda <ojeda@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Ingo Molnar <mingo@...nel.org>, Song Liu <song@...nel.org>,
Josh Poimboeuf <jpoimboe@...nel.org>
Subject: Re: [PATCH v2] ftrace: Allow inline functions not inlined to be
traced
On Fri, Jun 09, 2023 at 05:44:22PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
>
> Over 10 years ago there were many bugs that caused function tracing to
> crash because some inlined function was not inlined and should not have
> been traced. This made it hard to debug because when the developer tried
> to reproduce it, if their compiler still inlined the function, the bug
> would not trigger. The solution back then was simply to add "notrace" to
> "inline" which would make sure all functions that are marked inline are
> never traced even when the compiler decides to not inline them.
>
> A lot has changed over the last 10 years.
>
> 1) ftrace_test_recursion_trylock() is now used by all ftrace hooks which
> will prevent the recursive crashes from happening that was caused by
> inlined functions being traced.
>
> 2) noinstr is now used to mark pretty much all functions that would also
> cause problems if they are traced.
>
> Today, it is no longer a problem if an inlined function is not inlined and
> is traced, at least on x86. Removing notrace from inline has been requested
> several times over the years. I believe it is now safe to do so.
>
> Currently only x86 uses this.
>
> Acked-by: Song Liu <song@...nel.org>
> Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Acked-by: Mark Rutland <mark.rutland@....com>
> ---
> Changes since v1: https://lore.kernel.org/linux-trace-kernel/20230502164102.1a51cdb4@gandalf.local.home
>
> - have it opted in by architecture. Currently only x86 adds it. (Mark Rutland)
I'll add auditing/fixing arm64 on my queue of things to do; thanks for adding
the config option in the mean time!
Mark.
>
> arch/x86/Kconfig | 1 +
> include/linux/compiler_types.h | 16 +++++++++++++---
> kernel/trace/Kconfig | 7 +++++++
> 3 files changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index da5c081d64a5..1ddebf832534 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -61,6 +61,7 @@ config X86
> select ACPI_LEGACY_TABLES_LOOKUP if ACPI
> select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> select ARCH_32BIT_OFF_T if X86_32
> + select ARCH_CAN_TRACE_INLINE
> select ARCH_CLOCKSOURCE_INIT
> select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
> select ARCH_ENABLE_HUGEPAGE_MIGRATION if X86_64 && HUGETLB_PAGE && MIGRATION
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 547ea1ff806e..f827e2a98500 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -169,6 +169,16 @@ struct ftrace_likely_data {
> #define notrace __attribute__((__no_instrument_function__))
> #endif
>
> +/*
> + * If all inline code not marked as __always_inline is safe to trace,
> + * then allow the architecture to do so.
> + */
> +#ifdef CONFIG_ARCH_CAN_TRACE_INLINE
> +#define __notrace_inline
> +#else
> +#define __notrace_inline notrace
> +#endif
> +
> /*
> * it doesn't make sense on ARM (currently the only user of __naked)
> * to trace naked functions because then mcount is called without
> @@ -184,7 +194,7 @@ struct ftrace_likely_data {
> * of extern inline functions at link time.
> * A lot of inline functions can cause havoc with function tracing.
> */
> -#define inline inline __gnu_inline __inline_maybe_unused notrace
> +#define inline inline __gnu_inline __inline_maybe_unused __notrace_inline
>
> /*
> * gcc provides both __inline__ and __inline as alternate spellings of
> @@ -230,7 +240,7 @@ struct ftrace_likely_data {
> * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
> * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
> */
> -# define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
> +# define __no_kasan_or_inline __no_sanitize_address __notrace_inline __maybe_unused
> # define __no_sanitize_or_inline __no_kasan_or_inline
> #else
> # define __no_kasan_or_inline __always_inline
> @@ -247,7 +257,7 @@ struct ftrace_likely_data {
> * disable all instrumentation. See Kconfig.kcsan where this is mandatory.
> */
> # define __no_kcsan __no_sanitize_thread __disable_sanitizer_instrumentation
> -# define __no_sanitize_or_inline __no_kcsan notrace __maybe_unused
> +# define __no_sanitize_or_inline __no_kcsan __notrace_inline __maybe_unused
> #else
> # define __no_kcsan
> #endif
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index abe5c583bd59..b66ab0e6ce19 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -106,6 +106,13 @@ config HAVE_BUILDTIME_MCOUNT_SORT
> An architecture selects this if it sorts the mcount_loc section
> at build time.
>
> +config ARCH_CAN_TRACE_INLINE
> + bool
> + help
> + It is safe for an architecture to trace any function marked
> + as inline (not __always_inline) that the compiler decides to
> + not inline.
> +
> config BUILDTIME_MCOUNT_SORT
> bool
> default y
> --
> 2.39.2
>
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