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tracing: Init current_trace to nop_trace and remove NULL checks

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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: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Red Hat) 2013-02-01 18:38:47 -05:00 committed by Steven Rostedt
parent c1043fcda1
commit d840f718d2
1 changed files with 12 additions and 18 deletions
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30
kernel/trace/trace.c
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@ -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.
@ -2100,8 +2100,7 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter)
unsigned long total;
const char *name = "preemption";
if (type)
name = type->name;
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;
*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");
r = sprintf(buf, "%s\n", current_trace->name);
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) {
@ -3373,8 +3368,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
ret = -ENOMEM;
goto fail;
}
if (current_trace)
*iter->trace = *current_trace;
*iter->trace = *current_trace;
if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) {
ret = -ENOMEM;
@ -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;