tracing: Fix tp_printk option related with tp_printk_stop_on_boot

[ Upstream commit 3203ce39ac ]

The kernel parameter "tp_printk_stop_on_boot" starts with "tp_printk" which is
the same as another kernel parameter "tp_printk". If "tp_printk" setup is
called before the "tp_printk_stop_on_boot", it will override the latter
and keep it from being set.

This is similar to other kernel parameter issues, such as:
  Commit 745a600cf1 ("um: console: Ignore console= option")
or init/do_mounts.c:45 (setup function of "ro" kernel param)

Fix it by checking for a "_" right after the "tp_printk" and if that
exists do not process the parameter.

Link: https://lkml.kernel.org/r/20220208195421.969326-1-jsyoo5b@gmail.com

Signed-off-by: JaeSang Yoo <jsyoo5b@gmail.com>
[ Fixed up change log and added space after if condition ]
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

kernel/trace/trace.c

@@ -250,6 +250,10 @@ __setup("trace_clock=", set_trace_boot_clock);
 
 static int __init set_tracepoint_printk(char *str)
 {
+	/* Ignore the "tp_printk_stop_on_boot" param */
+	if (*str == '_')
+		return 0;
+
 	if ((strcmp(str, "=0") != 0 && strcmp(str, "=off") != 0))
 		tracepoint_printk = 1;
 	return 1;