4 files changed, 83 insertions, 41 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index b3d34d3e0e7e..8700049fd0e5 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -945,6 +945,10 @@ extern int __disable_trace_on_warning;
 #define INIT_TRACE_RECURSION            .trace_recursion = 0,
 #endif
 
+int tracepoint_printk_sysctl(struct ctl_table *table, int write,
+                             void __user *buffer, size_t *lenp,
+                             loff_t *ppos);
+
 #else /* CONFIG_TRACING */
 static inline void  disable_trace_on_warning(void) { }
 #endif /* CONFIG_TRACING */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 706309f9ed84..6ccc60dfbc7a 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -634,7 +634,7 @@ static struct ctl_table kern_table[] = {
                 .data           = &tracepoint_printk,
                 .maxlen         = sizeof(tracepoint_printk),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec,
+                .proc_handler   = tracepoint_printk_sysctl,
         },
 #endif
 #ifdef CONFIG_KEXEC_CORE
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 490533726b54..725e8b2c453f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -69,6 +69,7 @@ bool __read_mostly tracing_selftest_disabled;
 /* Pipe tracepoints to printk */
 struct trace_iterator *tracepoint_print_iter;
 int tracepoint_printk;
+static DEFINE_STATIC_KEY_FALSE(tracepoint_printk_key);
 
 /* For tracers that don't implement custom flags */
 static struct tracer_opt dummy_tracer_opt[] = {
@@ -2116,6 +2117,81 @@ trace_event_buffer_lock_reserve(struct ring_buffer **current_rb,
 }
 EXPORT_SYMBOL_GPL(trace_event_buffer_lock_reserve);
 
+static DEFINE_SPINLOCK(tracepoint_iter_lock);
+static DEFINE_MUTEX(tracepoint_printk_mutex);
+
+static void output_printk(struct trace_event_buffer *fbuffer)
+{
+        struct trace_event_call *event_call;
+        struct trace_event *event;
+        unsigned long flags;
+        struct trace_iterator *iter = tracepoint_print_iter;
+
+        /* We should never get here if iter is NULL */
+        if (WARN_ON_ONCE(!iter))
+                return;
+
+        event_call = fbuffer->trace_file->event_call;
+        if (!event_call || !event_call->event.funcs ||
+            !event_call->event.funcs->trace)
+                return;
+
+        event = &fbuffer->trace_file->event_call->event;
+
+        spin_lock_irqsave(&tracepoint_iter_lock, flags);
+        trace_seq_init(&iter->seq);
+        iter->ent = fbuffer->entry;
+        event_call->event.funcs->trace(iter, 0, event);
+        trace_seq_putc(&iter->seq, 0);
+        printk("%s", iter->seq.buffer);
+
+        spin_unlock_irqrestore(&tracepoint_iter_lock, flags);
+}
+
+int tracepoint_printk_sysctl(struct ctl_table *table, int write,
+                             void __user *buffer, size_t *lenp,
+                             loff_t *ppos)
+{
+        int save_tracepoint_printk;
+        int ret;
+
+        mutex_lock(&tracepoint_printk_mutex);
+        save_tracepoint_printk = tracepoint_printk;
+
+        ret = proc_dointvec(table, write, buffer, lenp, ppos);
+
+        /*
+         * This will force exiting early, as tracepoint_printk
+         * is always zero when tracepoint_printk_iter is not allocated
+         */
+        if (!tracepoint_print_iter)
+                tracepoint_printk = 0;
+
+        if (save_tracepoint_printk == tracepoint_printk)
+                goto out;
+
+        if (tracepoint_printk)
+                static_key_enable(&tracepoint_printk_key.key);
+        else
+                static_key_disable(&tracepoint_printk_key.key);
+
+ out:
+        mutex_unlock(&tracepoint_printk_mutex);
+
+        return ret;
+}
+
+void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
+{
+        if (static_key_false(&tracepoint_printk_key.key))
+                output_printk(fbuffer);
+
+        event_trigger_unlock_commit(fbuffer->trace_file, fbuffer->buffer,
+                                    fbuffer->event, fbuffer->entry,
+                                    fbuffer->flags, fbuffer->pc);
+}
+EXPORT_SYMBOL_GPL(trace_event_buffer_commit);
+
 void trace_buffer_unlock_commit_regs(struct trace_array *tr,
                                      struct ring_buffer *buffer,
                                      struct ring_buffer_event *event,
@@ -7977,6 +8053,8 @@ void __init trace_init(void)
                         kmalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
                 if (WARN_ON(!tracepoint_print_iter))
                         tracepoint_printk = 0;
+                else
+                        static_key_enable(&tracepoint_printk_key.key);
         }
         tracer_alloc_buffers();
         trace_event_init();
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index ba67ede48822..d35fc2b0d304 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -283,46 +283,6 @@ void *trace_event_buffer_reserve(struct trace_event_buffer *fbuffer,
 }
 EXPORT_SYMBOL_GPL(trace_event_buffer_reserve);
 
-static DEFINE_SPINLOCK(tracepoint_iter_lock);
-
-static void output_printk(struct trace_event_buffer *fbuffer)
-{
-        struct trace_event_call *event_call;
-        struct trace_event *event;
-        unsigned long flags;
-        struct trace_iterator *iter = tracepoint_print_iter;
-
-        if (!iter)
-                return;
-
-        event_call = fbuffer->trace_file->event_call;
-        if (!event_call || !event_call->event.funcs ||
-            !event_call->event.funcs->trace)
-                return;
-
-        event = &fbuffer->trace_file->event_call->event;
-
-        spin_lock_irqsave(&tracepoint_iter_lock, flags);
-        trace_seq_init(&iter->seq);
-        iter->ent = fbuffer->entry;
-        event_call->event.funcs->trace(iter, 0, event);
-        trace_seq_putc(&iter->seq, 0);
-        printk("%s", iter->seq.buffer);
-
-        spin_unlock_irqrestore(&tracepoint_iter_lock, flags);
-}
-
-void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
-{
-        if (tracepoint_printk)
-                output_printk(fbuffer);
-
-        event_trigger_unlock_commit(fbuffer->trace_file, fbuffer->buffer,
-                                    fbuffer->event, fbuffer->entry,
-                                    fbuffer->flags, fbuffer->pc);
-}
-EXPORT_SYMBOL_GPL(trace_event_buffer_commit);
-
 int trace_event_reg(struct trace_event_call *call,
                     enum trace_reg type, void *data)
 {