diff mbox series

[v2,33/44] ftrace: WARN on rcuidle

Message ID 20220919101522.573936213@infradead.org (mailing list archive)
State New, archived
Headers show
Series cpuidle,rcu: Clean up the mess | expand

Commit Message

Peter Zijlstra Sept. 19, 2022, 10 a.m. UTC
CONFIG_GENERIC_ENTRY disallows any and all tracing when RCU isn't
enabled.

XXX if s390 (the only other GENERIC_ENTRY user as of this writing)
isn't comfortable with this, we could switch to
HAVE_NOINSTR_VALIDATION which is x86_64 only atm.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/tracepoint.h |   13 ++++++++++++-
 kernel/trace/trace.c       |    3 +++
 2 files changed, 15 insertions(+), 1 deletion(-)

Comments

Steven Rostedt Sept. 26, 2022, 6:41 p.m. UTC | #1
Nit, the subject should have "tracing:" an not "ftrace:" as the former
encompasses the tracing infrastructure and the latter is for the function
hook part of that.

On Mon, 19 Sep 2022 12:00:12 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> CONFIG_GENERIC_ENTRY disallows any and all tracing when RCU isn't
> enabled.
> 
> XXX if s390 (the only other GENERIC_ENTRY user as of this writing)
> isn't comfortable with this, we could switch to
> HAVE_NOINSTR_VALIDATION which is x86_64 only atm.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/linux/tracepoint.h |   13 ++++++++++++-
>  kernel/trace/trace.c       |    3 +++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -178,6 +178,16 @@ static inline struct tracepoint *tracepo
>  #endif /* CONFIG_HAVE_STATIC_CALL */
>  
>  /*
> + * CONFIG_GENERIC_ENTRY archs are expected to have sanitized entry and idle
> + * code that disallow any/all tracing/instrumentation when RCU isn't watching.
> + */
> +#ifdef CONFIG_GENERIC_ENTRY
> +#define RCUIDLE_COND(rcuidle)	(rcuidle)
> +#else

Should probably move the below comment to here:

 /* srcu can't be used from NMI */

> +#define RCUIDLE_COND(rcuidle)	(rcuidle && in_nmi())
> +#endif
> +
> +/*
>   * it_func[0] is never NULL because there is at least one element in the array
>   * when the array itself is non NULL.
>   */
> @@ -189,7 +199,8 @@ static inline struct tracepoint *tracepo
>  			return;						\
>  									\
>  		/* srcu can't be used from NMI */			\

And remove the above.

-- Steve

> -		WARN_ON_ONCE(rcuidle && in_nmi());			\
> +		if (WARN_ON_ONCE(RCUIDLE_COND(rcuidle)))		\
> +			return;						\
>  									\
>  		/* keep srcu and sched-rcu usage consistent */		\
>  		preempt_disable_notrace();				\
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3104,6 +3104,9 @@ void __trace_stack(struct trace_array *t
>  		return;
>  	}
>  
> +	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_GENERIC_ENTRY)))
> +		return;
> +
>  	/*
>  	 * When an NMI triggers, RCU is enabled via ct_nmi_enter(),
>  	 * but if the above rcu_is_watching() failed, then the NMI
>
Mark Rutland Oct. 4, 2022, 5:19 p.m. UTC | #2
On Mon, Sep 19, 2022 at 12:00:12PM +0200, Peter Zijlstra wrote:
> CONFIG_GENERIC_ENTRY disallows any and all tracing when RCU isn't
> enabled.
> 
> XXX if s390 (the only other GENERIC_ENTRY user as of this writing)
> isn't comfortable with this, we could switch to
> HAVE_NOINSTR_VALIDATION which is x86_64 only atm.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/linux/tracepoint.h |   13 ++++++++++++-
>  kernel/trace/trace.c       |    3 +++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -178,6 +178,16 @@ static inline struct tracepoint *tracepo
>  #endif /* CONFIG_HAVE_STATIC_CALL */
>  
>  /*
> + * CONFIG_GENERIC_ENTRY archs are expected to have sanitized entry and idle
> + * code that disallow any/all tracing/instrumentation when RCU isn't watching.
> + */
> +#ifdef CONFIG_GENERIC_ENTRY
> +#define RCUIDLE_COND(rcuidle)	(rcuidle)
> +#else
> +#define RCUIDLE_COND(rcuidle)	(rcuidle && in_nmi())
> +#endif

Could we make this depend on ARCH_WANTS_NO_INSTR instead?

That'll allow arm64 to check this even though we're not using the generic entry
code (and there's lots of work necessary to make that possible...).

Thanks,
Mark.

> +
> +/*
>   * it_func[0] is never NULL because there is at least one element in the array
>   * when the array itself is non NULL.
>   */
> @@ -189,7 +199,8 @@ static inline struct tracepoint *tracepo
>  			return;						\
>  									\
>  		/* srcu can't be used from NMI */			\
> -		WARN_ON_ONCE(rcuidle && in_nmi());			\
> +		if (WARN_ON_ONCE(RCUIDLE_COND(rcuidle)))		\
> +			return;						\
>  									\
>  		/* keep srcu and sched-rcu usage consistent */		\
>  		preempt_disable_notrace();				\
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3104,6 +3104,9 @@ void __trace_stack(struct trace_array *t
>  		return;
>  	}
>  
> +	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_GENERIC_ENTRY)))
> +		return;
> +
>  	/*
>  	 * When an NMI triggers, RCU is enabled via ct_nmi_enter(),
>  	 * but if the above rcu_is_watching() failed, then the NMI
> 
>
diff mbox series

Patch

--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -178,6 +178,16 @@  static inline struct tracepoint *tracepo
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
 /*
+ * CONFIG_GENERIC_ENTRY archs are expected to have sanitized entry and idle
+ * code that disallow any/all tracing/instrumentation when RCU isn't watching.
+ */
+#ifdef CONFIG_GENERIC_ENTRY
+#define RCUIDLE_COND(rcuidle)	(rcuidle)
+#else
+#define RCUIDLE_COND(rcuidle)	(rcuidle && in_nmi())
+#endif
+
+/*
  * it_func[0] is never NULL because there is at least one element in the array
  * when the array itself is non NULL.
  */
@@ -189,7 +199,8 @@  static inline struct tracepoint *tracepo
 			return;						\
 									\
 		/* srcu can't be used from NMI */			\
-		WARN_ON_ONCE(rcuidle && in_nmi());			\
+		if (WARN_ON_ONCE(RCUIDLE_COND(rcuidle)))		\
+			return;						\
 									\
 		/* keep srcu and sched-rcu usage consistent */		\
 		preempt_disable_notrace();				\
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3104,6 +3104,9 @@  void __trace_stack(struct trace_array *t
 		return;
 	}
 
+	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_GENERIC_ENTRY)))
+		return;
+
 	/*
 	 * When an NMI triggers, RCU is enabled via ct_nmi_enter(),
 	 * but if the above rcu_is_watching() failed, then the NMI