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>

5 files changed, 26 insertions, 14 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index f98c4076a170..1b43086b097a 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -476,7 +476,10 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
                                 &return_to_handler;
 
         /* Nmi's are currently unsupported */
-        if (atomic_read(&in_nmi))
+        if (unlikely(atomic_read(&in_nmi)))
+                return;
+
+        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                 return;
 
         /*
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 449fa8e9e34f..11cac81eed08 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -401,6 +401,16 @@ static inline int task_curr_ret_stack(struct task_struct *t)
 {
         return t->curr_ret_stack;
 }
+
+static inline void pause_graph_tracing(void)
+{
+        atomic_inc(&current->tracing_graph_pause);
+}
+
+static inline void unpause_graph_tracing(void)
+{
+        atomic_dec(&current->tracing_graph_pause);
+}
 #else
 
 #define __notrace_funcgraph
@@ -412,6 +422,9 @@ static inline int task_curr_ret_stack(struct task_struct *tsk)
 {
         return -1;
 }
+
+static inline void pause_graph_tracing(void) { }
+static inline void unpause_graph_tracing(void) { }
 #endif
 
 #ifdef CONFIG_TRACING
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4c152e0acc9e..4b81fc5f7731 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1379,6 +1379,8 @@ struct task_struct {
          * because of depth overrun.
          */
         atomic_t trace_overrun;
+        /* Pause for the tracing */
+        atomic_t tracing_graph_pause;
 #endif
 #ifdef CONFIG_TRACING
         /* state flags for use by tracers */
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2971fe48f55e..a12f80efceaa 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 33549537f30f..0b8659bd5ad2 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();