tracing: Ignore mmiotrace from kernel commandline

The mmiotrace tracer cannot be enabled with ftrace=mmiotrace in kernel
commandline. With this patch, noboot is added to the tracer struct,
and when system boot with a tracer that has noboot=true, it will print
out a warning message and continue booting.

Link: http://lkml.kernel.org/r/1505111195-31942-1-git-send-email-zsun@redhat.com

Signed-off-by: Ziqian SUN (Zamir) <zsun@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

3 files changed, 10 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a7fb136da891..d3ca35f38803 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5364,6 +5364,13 @@ static int tracing_set_tracer(struct trace_array *tr, const char *buf)
         if (t == tr->current_trace)
                 goto out;
 
+        /* Some tracers won't work on kernel command line */
+        if (system_state < SYSTEM_RUNNING && t->noboot) {
+                pr_warn("Tracer '%s' is not allowed on command line, ignored\n",
+                        t->name);
+                goto out;
+        }
+
         /* Some tracers are only allowed for the top level buffer */
         if (!trace_ok_for_array(t, tr)) {
                 ret = -EINVAL;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index fb5d54d0d1b3..652c682707cd 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -444,6 +444,8 @@ struct tracer {
 #ifdef CONFIG_TRACER_MAX_TRACE
         bool                    use_max_tr;
 #endif
+        /* True if tracer cannot be enabled in kernel param */
+        bool                    noboot;
 };
 
 
diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index cd7480d0a201..dca78fc48439 100644
--- a/kernel/trace/trace_mmiotrace.c
+++ b/kernel/trace/trace_mmiotrace.c
@@ -282,6 +282,7 @@ static struct tracer mmio_tracer __read_mostly =
         .close          = mmio_close,
         .read           = mmio_read,
         .print_line     = mmio_print_line,
+        .noboot         = true,
 };
 
 __init static int init_mmio_trace(void)