>From 8260b0308d3ee0f836cd5ea4b177efeb52ab151f Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" <rost...@goodmis.org> Date: Fri, 12 May 2017 13:15:45 -0400 Subject: [PATCH] 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/20170512172449.879684...@goodmis.org Cc: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org> --- Changes since v2: Use rcu_is_watching() instead if checking for in_nmi() and irqs disabled. But now if rcu_is_watching() fails and in_nmi() is true, bail. kernel/trace/trace.c | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index fcc9a2d..1122f15 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(); } /** -- 2.9.3
