tracing: Have trace_array keep track if snapshot buffer is allocated

The snapshot buffer belongs to the trace array not the tracer that is
running. The trace array should be the data structure that keeps track
of whether or not the snapshot buffer is allocated, not the tracer
desciptor. Having the trace array keep track of it makes modifications
so much easier.

Signed-off-by: Steven Rostedt <[email protected]>

Author: Steven Rostedt (Red Hat)

kernel/trace/trace.c

@@ -667,7 +667,7 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 
 	WARN_ON_ONCE(!irqs_disabled());
 
-	if (!tr->current_trace->allocated_snapshot) {
+	if (!tr->allocated_snapshot) {
 		/* Only the nop tracer should hit this when disabling */
 		WARN_ON_ONCE(tr->current_trace != &nop_trace);
 		return;
@@ -700,7 +700,7 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
 		return;
 
 	WARN_ON_ONCE(!irqs_disabled());
-	if (WARN_ON_ONCE(!tr->current_trace->allocated_snapshot))
+	if (WARN_ON_ONCE(!tr->allocated_snapshot))
 		return;
 
 	arch_spin_lock(&ftrace_max_lock);
@@ -802,7 +802,7 @@ int register_tracer(struct tracer *type)
 			if (ring_buffer_expanded)
 				ring_buffer_resize(tr->max_buffer.buffer, trace_buf_size,
 						   RING_BUFFER_ALL_CPUS);
-			type->allocated_snapshot = true;
+			tr->allocated_snapshot = true;
 		}
 #endif
 
@@ -822,7 +822,7 @@ int register_tracer(struct tracer *type)
 
 #ifdef CONFIG_TRACER_MAX_TRACE
 		if (type->use_max_tr) {
-			type->allocated_snapshot = false;
+			tr->allocated_snapshot = false;
 
 			/* Shrink the max buffer again */
 			if (ring_buffer_expanded)
@@ -2463,7 +2463,7 @@ static void show_snapshot_percpu_help(struct seq_file *m)
 
 static void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter)
 {
-	if (iter->trace->allocated_snapshot)
+	if (iter->tr->allocated_snapshot)
 		seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
 	else
 		seq_printf(m, "#\n# * Snapshot is freed *\n#\n");
@@ -3364,12 +3364,12 @@ static int tracing_set_tracer(const char *buf)
 	if (tr->current_trace->reset)
 		tr->current_trace->reset(tr);
 
-#ifdef CONFIG_TRACER_MAX_TRACE
-	had_max_tr = tr->current_trace->allocated_snapshot;
-
 	/* Current trace needs to be nop_trace before synchronize_sched */
 	tr->current_trace = &nop_trace;
 
+#ifdef CONFIG_TRACER_MAX_TRACE
+	had_max_tr = tr->allocated_snapshot;
+
 	if (had_max_tr && !t->use_max_tr) {
 		/*
 		 * We need to make sure that the update_max_tr sees that
@@ -3387,10 +3387,8 @@ static int tracing_set_tracer(const char *buf)
 		ring_buffer_resize(tr->max_buffer.buffer, 1, RING_BUFFER_ALL_CPUS);
 		set_buffer_entries(&tr->max_buffer, 1);
 		tracing_reset_online_cpus(&tr->max_buffer);
-		tr->current_trace->allocated_snapshot = false;
+		tr->allocated_snapshot = false;
 	}
-#else
-	tr->current_trace = &nop_trace;
 #endif
 	destroy_trace_option_files(topts);
 
@@ -3403,7 +3401,7 @@ static int tracing_set_tracer(const char *buf)
 						   RING_BUFFER_ALL_CPUS);
 		if (ret < 0)
 			goto out;
-		t->allocated_snapshot = true;
+		tr->allocated_snapshot = true;
 	}
 #endif
 
@@ -4275,13 +4273,13 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 			ret = -EINVAL;
 			break;
 		}
-		if (tr->current_trace->allocated_snapshot) {
+		if (tr->allocated_snapshot) {
 			/* free spare buffer */
 			ring_buffer_resize(tr->max_buffer.buffer, 1,
 					   RING_BUFFER_ALL_CPUS);
 			set_buffer_entries(&tr->max_buffer, 1);
 			tracing_reset_online_cpus(&tr->max_buffer);
-			tr->current_trace->allocated_snapshot = false;
+			tr->allocated_snapshot = false;
 		}
 		break;
 	case 1:
@@ -4292,13 +4290,13 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 			break;
 		}
 #endif
-		if (!tr->current_trace->allocated_snapshot) {
+		if (!tr->allocated_snapshot) {
 			/* allocate spare buffer */
 			ret = resize_buffer_duplicate_size(&tr->max_buffer,
 					&tr->trace_buffer, RING_BUFFER_ALL_CPUS);
 			if (ret < 0)
 				break;
-			tr->current_trace->allocated_snapshot = true;
+			tr->allocated_snapshot = true;
 		}
 		local_irq_disable();
 		/* Now, we're going to swap */
@@ -4309,7 +4307,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 		local_irq_enable();
 		break;
 	default:
-		if (tr->current_trace->allocated_snapshot) {
+		if (tr->allocated_snapshot) {
 			if (iter->cpu_file == RING_BUFFER_ALL_CPUS)
 				tracing_reset_online_cpus(&tr->max_buffer);
 			else

kernel/trace/trace.h

@@ -197,6 +197,7 @@ struct trace_array {
 	 * the trace_buffer so the tracing can continue.
 	 */
 	struct trace_buffer	max_buffer;
+	bool			allocated_snapshot;
 #endif
 	int			buffer_disabled;
 	struct trace_cpu	trace_cpu;	/* place holder */
@@ -367,7 +368,6 @@ struct tracer {
 	bool			enabled;
 #ifdef CONFIG_TRACER_MAX_TRACE
 	bool			use_max_tr;
-	bool			allocated_snapshot;
 #endif
 };