tracing: Add stack_tracer_disable/enable() functions

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>

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ef7123219f14ace625b13631220bea78be6ad567..7b4e6572ab21d5f98a0a09641f5dda193cefbf03 100644 (file)
--- 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_enable(void) { }
 #endif
 
 struct ftrace_func_command {

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 338d076a06da8d0f65416ec1ef706b5714f739c4..21e536cf66e42f33750aff96d2af202db4a41e6c 100644 (file)
--- 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;