linux-kernel - [PATCH v2 3/9] tracing: Warn about !rcu_is

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Message-ID: <20230126151323.466670589@infradead.org>
Date:   Thu, 26 Jan 2023 16:08:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org
Cc:     will@...nel.org, peterz@...radead.org, boqun.feng@...il.com,
        mark.rutland@....com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, seanjc@...gle.com, pbonzini@...hat.com,
        jgross@...e.com, srivatsa@...il.mit.edu, amakhalov@...are.com,
        pv-drivers@...are.com, wanpengli@...cent.com, vkuznets@...hat.com,
        boris.ostrovsky@...cle.com, rafael@...nel.org,
        daniel.lezcano@...aro.org, lpieralisi@...nel.org,
        frederic@...nel.org, paulmck@...nel.org, rostedt@...dmis.org,
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        vincent.guittot@...aro.org, dietmar.eggemann@....com,
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        vschneid@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        linux-pm@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: [PATCH v2 3/9] tracing: Warn about !rcu_is_watching()

When using noinstr, WARN when tracing hits when RCU is disabled.

Suggested-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/linux/trace_recursion.h |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/include/linux/trace_recursion.h
+++ b/include/linux/trace_recursion.h
@@ -135,6 +135,21 @@ extern void ftrace_record_recursion(unsi
 # define do_ftrace_record_recursion(ip, pip)	do { } while (0)
 #endif
 
+#ifdef CONFIG_ARCH_WANTS_NO_INSTR
+# define trace_warn_on_no_rcu(ip)					\
+	({								\
+		bool __ret = !rcu_is_watching();			\
+		if (__ret && !trace_recursion_test(TRACE_RECORD_RECURSION_BIT)) { \
+			trace_recursion_set(TRACE_RECORD_RECURSION_BIT); \
+			WARN_ONCE(true, "RCU not on for: %pS\n", (void *)ip); \
+			trace_recursion_clear(TRACE_RECORD_RECURSION_BIT); \
+		}							\
+		__ret;							\
+	})
+#else
+# define trace_warn_on_no_rcu(ip)	false
+#endif
+
 /*
  * Preemption is promised to be disabled when return bit >= 0.
  */
@@ -144,6 +159,9 @@ static __always_inline int trace_test_an
 	unsigned int val = READ_ONCE(current->trace_recursion);
 	int bit;
 
+	if (trace_warn_on_no_rcu(ip))
+		return -1;
+
 	bit = trace_get_context_bit() + start;
 	if (unlikely(val & (1 << bit))) {
 		/*