Thread (88 messages) 88 messages, 13 authors, 2022-11-22

Re: [PATCH v2 33/44] ftrace: WARN on rcuidle

From: Steven Rostedt <rostedt@goodmis.org>
Date: 2022-09-26 18:43:00
Also in: linux-acpi, linux-alpha, linux-arch, linux-arm-msm, linux-clk, linux-m68k, linux-mips, linux-omap, linux-perf-users, linux-pm, linux-riscv, linux-s390, linux-sh, linux-tegra, linux-um, lkml, loongarch, sparclinux, virtualization

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 [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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 */
quoted hunk ↗ jump to hunk
+#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
quoted hunk ↗ jump to hunk
-		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
  
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