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Groups > linux.kernel > #1618826

[PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable() functions

From Steven Rostedt <rostedt@goodmis.org>
Newsgroups linux.kernel
Subject [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable() functions
Date 2017-04-07 16:10 +0200
Message-ID <ttCKn-8a9-39@gated-at.bofh.it> (permalink)
References <ttCKl-8a9-13@gated-at.bofh.it>
Organization linux.* mail to news gateway

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

There are certain parts of the kernel that cannot let stack tracing
proceed (namely in RCU), because the stack tracer uses RCU, and parts of RCU
internals cannot handle having RCU read side locks taken.

Add stack_tracer_disable() and stack_tracer_enable() functions to let RCU
stop stack tracing on the current CPU when it is in those critical sections.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/ftrace.h     |  6 ++++++
 kernel/trace/trace_stack.c | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ef7123219f14..40afee35565a 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -286,6 +286,12 @@ int
 stack_trace_sysctl(struct ctl_table *table, int write,
 		   void __user *buffer, size_t *lenp,
 		   loff_t *ppos);
+
+void stack_tracer_disable(void);
+void stack_tracer_enable(void);
+#else
+static inline void stack_tracer_disable(void) { }
+static inline void stack_tracer_enabe(void) { }
 #endif
 
 struct ftrace_func_command {
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 05ad2b86461e..7d52504680f9 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -41,6 +41,38 @@ static DEFINE_MUTEX(stack_sysctl_mutex);
 int stack_tracer_enabled;
 static int last_stack_tracer_enabled;
 
+/**
+ * stack_tracer_disable - temporarily disable the stack tracer
+ *
+ * There's a few locations (namely in RCU) where stack tracing
+ * cannot be executed. This function is used to disable stack
+ * tracing during those critical sections.
+ *
+ * This function must be called with preemption or interrupts
+ * disabled and stack_tracer_enable() must be called shortly after
+ * while preemption or interrupts are still disabled.
+ */
+void stack_tracer_disable(void)
+{
+	/* Preemption or interupts must be disabled */
+	if (IS_ENABLED(CONFIG_PREEMPT_DEBUG))
+		WARN_ON_ONCE(!preempt_count() || !irqs_disabled());
+	this_cpu_inc(trace_active);
+}
+
+/**
+ * stack_tracer_enable - re-enable the stack tracer
+ *
+ * After stack_tracer_disable() is called, stack_tracer_enable()
+ * must be called shortly afterward.
+ */
+void stack_tracer_enable(void)
+{
+	if (IS_ENABLED(CONFIG_PREEMPT_DEBUG))
+		WARN_ON_ONCE(!preempt_count() || !irqs_disabled());
+	this_cpu_dec(trace_active);
+}
+
 void stack_trace_print(void)
 {
 	long i;
-- 
2.10.2

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[PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks() and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
  [PATCH 1/5 v2] ftrace: Add use of synchronize_rcu_tasks() with dynamic trampolines Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
  [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable() functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
    [PATCH 3/5 v2.1] tracing: Add stack_tracer_disable/enable()  functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:30 +0200
    Re: [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable()  functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:30 +0200
  Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 16:50 +0200
    Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 17:10 +0200
      Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 17:20 +0200
        Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 17:30 +0200
  [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 18:40 +0200
    Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 18:50 +0200
      Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 18:50 +0200
        Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:00 +0200
      [PATCH 6/5 v2] rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:10 +0200
        Re: [PATCH 6/5 v2] rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:20 +0200
  [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:10 +0200
    Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:20 +0200
    Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 19:20 +0200
      Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:30 +0200
        Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:40 +0200
        Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 19:50 +0200
          Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 20:00 +0200
          [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 20:20 +0200
            Re: [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 20:20 +0200
              Re: [PATCH 7/5 v4] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 21:50 +0200
              [PATCH 7/5 v4] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 21:50 +0200
      Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:30 +0200
      [PATCH 7/5 v2] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:50 +0200

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