tracing: Make sure RCU is watching before calling a stack trace

As stack tracing now requires "rcu watching", force RCU to be watching when
recording a stack trace.

Link: http://lkml.kernel.org/r/20170512172449.879684501@goodmis.org

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 30 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index fcc9a2d774c3..1122f151466f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2568,7 +2568,36 @@ static inline void ftrace_trace_stack(struct trace_array *tr,
 void __trace_stack(struct trace_array *tr, unsigned long flags, int skip,
                    int pc)
 {
-        __ftrace_trace_stack(tr->trace_buffer.buffer, flags, skip, pc, NULL);
+        struct ring_buffer *buffer = tr->trace_buffer.buffer;
+
+        if (rcu_is_watching()) {
+                __ftrace_trace_stack(buffer, flags, skip, pc, NULL);
+                return;
+        }
+
+        /*
+         * When an NMI triggers, RCU is enabled via rcu_nmi_enter(),
+         * but if the above rcu_is_watching() failed, then the NMI
+         * triggered someplace critical, and rcu_irq_enter() should
+         * not be called from NMI.
+         */
+        if (unlikely(in_nmi()))
+                return;
+
+        /*
+         * It is possible that a function is being traced in a
+         * location that RCU is not watching. A call to
+         * rcu_irq_enter() will make sure that it is, but there's
+         * a few internal rcu functions that could be traced
+         * where that wont work either. In those cases, we just
+         * do nothing.
+         */
+        if (unlikely(rcu_irq_enter_disabled()))
+                return;
+
+        rcu_irq_enter_irqson();
+        __ftrace_trace_stack(buffer, flags, skip, pc, NULL);
+        rcu_irq_exit_irqson();
 }
 
 /**