3 files changed, 19 insertions, 3 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5360b7aec57a..752e5daf0896 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4020,11 +4020,17 @@ static int tracing_open(struct inode *inode, struct file *file)
         /* If this file was open for write, then erase contents */
         if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
                 int cpu = tracing_get_cpu(inode);
+                struct trace_buffer *trace_buf = &tr->trace_buffer;
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+                if (tr->current_trace->print_max)
+                        trace_buf = &tr->max_buffer;
+#endif
 
                 if (cpu == RING_BUFFER_ALL_CPUS)
-                        tracing_reset_online_cpus(&tr->trace_buffer);
+                        tracing_reset_online_cpus(trace_buf);
                 else
-                        tracing_reset(&tr->trace_buffer, cpu);
+                        tracing_reset(trace_buf, cpu);
         }
 
         if (file->f_mode & FMODE_READ) {
@@ -5358,6 +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;
@@ -5667,7 +5680,7 @@ static int tracing_wait_pipe(struct file *filp)
                  *
                  * iter->pos will be 0 if we haven't read anything.
                  */
-                if (!tracing_is_on() && iter->pos)
+                if (!tracer_tracing_is_on(iter->tr) && iter->pos)
                         break;
 
                 mutex_unlock(&iter->mutex);
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)