linux-kernel - [RFC][PATCH] tracing: Hide global trace clock from lockdep

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Date:   Wed, 4 Apr 2018 14:50:15 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [RFC][PATCH] tracing: Hide global trace clock from lockdep

From: Steven Rostedt (VMware) <rostedt@...dmis.org>

Function tracing can trace in NMIs and such. If the TSC is determined
to be unstable, the tracing clock will switch to the global clock on
boot up, unless "trace_clock" is specified on the kernel command line.

The global clock disables interrupts to access sched_clock_cpu(), and in
doing so can be done within lockdep internals (because of function
tracing and NMIs). This can trigger false lockdep splats.

The trace_clock_global() is special, best not to trace the irq logic
within it.

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index 5fdc779f411d..d8a188e0418a 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -96,7 +96,7 @@ u64 notrace trace_clock_global(void)
 	int this_cpu;
 	u64 now;

-	local_irq_save(flags);
+	raw_local_irq_save(flags);

 	this_cpu = raw_smp_processor_id();
 	now = sched_clock_cpu(this_cpu);
@@ -122,7 +122,7 @@ u64 notrace trace_clock_global(void)
 	arch_spin_unlock(&trace_clock_struct.lock);

  out:
-	local_irq_restore(flags);
+	raw_local_irq_restore(flags);

 	return now;
 }