tracing/function-graph-tracer: append the tracing_graph_flag

Impact: Provide a way to pause the function graph tracer

As suggested by Steven Rostedt, the previous patch that prevented from
spinlock function tracing shouldn't use the raw_spinlock to fix it.
It's much better to follow lockdep with normal spinlock, so this patch
adds a new flag for each task to make the function graph tracer able
to be paused. We also can send an ftrace_printk whithout worrying of
the irrelevant traced spinlock during insertion.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 7 insertions, 13 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2971fe48f55..a12f80efcea 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1998,6 +1998,7 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
 			/* Make sure IRQs see the -1 first: */
 			barrier();
 			t->ret_stack = ret_stack_list[start++];
+			atomic_set(&t->tracing_graph_pause, 0);
 			atomic_set(&t->trace_overrun, 0);
 		}
 	} while_each_thread(g, t);
@@ -2077,6 +2078,7 @@ void ftrace_graph_init_task(struct task_struct *t)
 		if (!t->ret_stack)
 			return;
 		t->curr_ret_stack = -1;
+		atomic_set(&t->tracing_graph_pause, 0);
 		atomic_set(&t->trace_overrun, 0);
 	} else
 		t->ret_stack = NULL;
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 33549537f30..0b8659bd5ad 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3590,14 +3590,7 @@ static __init int tracer_init_debugfs(void)
 
 int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
 {
-	/*
-	 * Raw Spinlock because a normal spinlock would be traced here
-	 * and append an irrelevant couple spin_lock_irqsave/
-	 * spin_unlock_irqrestore traced by ftrace around this
-	 * TRACE_PRINTK trace.
-	 */
-	static raw_spinlock_t trace_buf_lock =
-				(raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+	static DEFINE_SPINLOCK(trace_buf_lock);
 	static char trace_buf[TRACE_BUF_SIZE];
 
 	struct ring_buffer_event *event;
@@ -3618,8 +3611,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
 	if (unlikely(atomic_read(&data->disabled)))
 		goto out;
 
-	local_irq_save(flags);
-	__raw_spin_lock(&trace_buf_lock);
+	pause_graph_tracing();
+	spin_lock_irqsave(&trace_buf_lock, irq_flags);
 	len = vsnprintf(trace_buf, TRACE_BUF_SIZE, fmt, args);
 
 	len = min(len, TRACE_BUF_SIZE-1);
@@ -3640,9 +3633,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
 	ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
 
  out_unlock:
-	__raw_spin_unlock(&trace_buf_lock);
-	local_irq_restore(flags);
-
+	spin_unlock_irqrestore(&trace_buf_lock, irq_flags);
+	unpause_graph_tracing();
  out:
 	preempt_enable_notrace();