Commit d840f718 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
Browse files

tracing: Init current_trace to nop_trace and remove NULL checks 



On early boot up, when the ftrace ring buffer is initialized, the
static variable current_trace is initialized to &nop_trace.
Before this initialization, current_trace is NULL and will never
become NULL again. It is always reassigned to a ftrace tracer.

Several places check if current_trace is NULL before it uses
it, and this check is frivolous, because at the point in time
when the checks are made the only way current_trace could be
NULL is if ftrace failed its allocations at boot up, and the
paths to these locations would probably not be possible.

By initializing current_trace to &nop_trace where it is declared,
current_trace will never be NULL, and we can remove all these
checks of current_trace being NULL which never needed to be
checked in the first place.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent c1043fcd

kernel/trace/trace.c

+12 −18
Original line number Diff line number Diff line
@@ -249,7 +249,7 @@ static unsigned long trace_buf_size = TRACE_BUF_SIZE_DEFAULT; 
static struct tracer		*trace_types __read_mostly;



/* current_trace points to the tracer that is currently active */

static struct tracer		*current_trace __read_mostly;

static struct tracer		*current_trace __read_mostly = &nop_trace;



/*

 * trace_types_lock is used to protect the trace_types list.
@@ -2100,7 +2100,6 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter) 
	unsigned long total;

	const char *name = "preemption";



	if (type)

	name = type->name;



	get_total_entries(tr, &total, &entries);
@@ -2477,13 +2476,12 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) 
	if (!iter->trace)

		goto fail;



	if (current_trace)

	*iter->trace = *current_trace;



	if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL))

		goto fail;



	if ((current_trace && current_trace->print_max) || snapshot)

	if (current_trace->print_max || snapshot)

		iter->tr = &max_tr;

	else

		iter->tr = &global_trace;
@@ -3037,10 +3035,7 @@ tracing_set_trace_read(struct file *filp, char __user *ubuf, 
	int r;



	mutex_lock(&trace_types_lock);

	if (current_trace)

	r = sprintf(buf, "%s\n", current_trace->name);

	else

		r = sprintf(buf, "\n");

	mutex_unlock(&trace_types_lock);



	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
@@ -3231,10 +3226,10 @@ static int tracing_set_tracer(const char *buf) 
		goto out;



	trace_branch_disable();

	if (current_trace && current_trace->reset)

	if (current_trace->reset)

		current_trace->reset(tr);



	had_max_tr = current_trace && current_trace->allocated_snapshot;

	had_max_tr = current_trace->allocated_snapshot;

	current_trace = &nop_trace;



	if (had_max_tr && !t->use_max_tr) {
@@ -3373,7 +3368,6 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) 
		ret = -ENOMEM;

		goto fail;

	}

	if (current_trace)

	*iter->trace = *current_trace;



	if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) {
@@ -3525,7 +3519,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, 


	/* copy the tracer to avoid using a global lock all around */

	mutex_lock(&trace_types_lock);

	if (unlikely(current_trace && iter->trace->name != current_trace->name))

	if (unlikely(iter->trace->name != current_trace->name))

		*iter->trace = *current_trace;

	mutex_unlock(&trace_types_lock);
@@ -3691,7 +3685,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp, 


	/* copy the tracer to avoid using a global lock all around */

	mutex_lock(&trace_types_lock);

	if (unlikely(current_trace && iter->trace->name != current_trace->name))

	if (unlikely(iter->trace->name != current_trace->name))

		*iter->trace = *current_trace;

	mutex_unlock(&trace_types_lock);
@@ -4115,7 +4109,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt, 


	mutex_lock(&trace_types_lock);



	if (current_trace && current_trace->use_max_tr) {

	if (current_trace->use_max_tr) {

		ret = -EBUSY;

		goto out;

	}
@@ -5299,7 +5293,7 @@ __init static int tracer_alloc_buffers(void) 
	init_irq_work(&trace_work_wakeup, trace_wake_up);



	register_tracer(&nop_trace);

	current_trace = &nop_trace;



	/* All seems OK, enable tracing */

	tracing_disabled = 0;

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