tracing: Do not stop recording cmdlines when tracing is off

stable inclusion
from linux-4.19.196
commit ae1fe292b314fbc1db9b1897d1f354c8f2e1931a

--------------------------------

commit 85550c83 upstream.

The saved_cmdlines is used to map pids to the task name, such that the
output of the tracing does not just show pids, but also gives a human
readable name for the task.

If the name is not mapped, the output looks like this:

    <...>-1316          [005] ...2   132.044039: ...

Instead of this:

    gnome-shell-1316    [005] ...2   132.044039: ...

The names are updated when tracing is running, but are skipped if tracing
is stopped. Unfortunately, this stops the recording of the names if the
top level tracer is stopped, and not if there's other tracers active.

The recording of a name only happens when a new event is written into a
ring buffer, so there is no need to test if tracing is on or not. If
tracing is off, then no event is written and no need to test if tracing is
off or not.

Remove the check, as it hides the names of tasks for events in the
instance buffers.

Cc: stable@vger.kernel.org
Fixes: 7ffbd48d ("tracing: Cache comms only after an event occurred")
Signed-off-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

kernel/trace/trace.c

@@ -2029,8 +2029,6 @@ static bool tracing_record_taskinfo_skip(int flags)
 {
 	if (unlikely(!(flags & (TRACE_RECORD_CMDLINE | TRACE_RECORD_TGID))))
 		return true;
-	if (atomic_read(&trace_record_taskinfo_disabled) || !tracing_is_on())
-		return true;
 	if (!__this_cpu_read(trace_taskinfo_save))
 		return true;
 	return false;