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Subject[for-next][PATCH] tracing: Make sure RCU is watching before calling a stack trace

I'll probably just push this to Linus tomorrow along with my other
changes.

-- Steve


git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
for-next

Head SHA1: a33d7d94eed92b23fbbc7b0de06a41b2bbaa49e3


Steven Rostedt (VMware) (1):
tracing: Make sure RCU is watching before calling a stack trace

----
kernel/trace/trace.c | 31 ++++++++++++++++++++++++++++++-
1 file changed, 30 insertions(+), 1 deletion(-)
---------------------------
commit a33d7d94eed92b23fbbc7b0de06a41b2bbaa49e3
Author: Steven Rostedt (VMware) <rostedt@goodmis.org>
Date: Fri May 12 13:15:45 2017 -0400

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>

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();
}

/**
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