3 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index e061b4ecdc3a..5fcc31ed5771 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -140,8 +140,17 @@ unsigned long ring_buffer_size(struct ring_buffer *buffer);
 void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu);
 void ring_buffer_reset(struct ring_buffer *buffer);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
                          struct ring_buffer *buffer_b, int cpu);
+#else
+static inline int
+ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
+                     struct ring_buffer *buffer_b, int cpu)
+{
+        return -ENODEV;
+}
+#endif
 
 int ring_buffer_empty(struct ring_buffer *buffer);
 int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu);
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 163fbfc2f39f..1ea0d1234f4a 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -62,6 +62,12 @@ config EVENT_TRACING
 config CONTEXT_SWITCH_TRACER
         bool
 
+config RING_BUFFER_ALLOW_SWAP
+        bool
+        help
+         Allow the use of ring_buffer_swap_cpu.
+         Adds a very slight overhead to tracing when enabled.
+
 # All tracer options should select GENERIC_TRACER. For those options that are
 # enabled by all tracers (context switch and event tracer) they select TRACING.
 # This allows those options to appear when no other tracer is selected. But the
@@ -146,6 +152,7 @@ config IRQSOFF_TRACER
         select TRACE_IRQFLAGS
         select GENERIC_TRACER
         select TRACER_MAX_TRACE
+        select RING_BUFFER_ALLOW_SWAP
         help
           This option measures the time spent in irqs-off critical
           sections, with microsecond accuracy.
@@ -167,6 +174,7 @@ config PREEMPT_TRACER
         depends on PREEMPT
         select GENERIC_TRACER
         select TRACER_MAX_TRACE
+        select RING_BUFFER_ALLOW_SWAP
         help
           This option measures the time spent in preemption off critical
           sections, with microsecond accuracy.
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 1766c0e8db5a..454e74e718cf 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2084,6 +2084,7 @@ rb_reserve_next_event(struct ring_buffer *buffer,
 
         rb_start_commit(cpu_buffer);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
         /*
          * Due to the ability to swap a cpu buffer from a buffer
          * it is possible it was swapped before we committed.
@@ -2096,6 +2097,7 @@ rb_reserve_next_event(struct ring_buffer *buffer,
                 local_dec(&cpu_buffer->commits);
                 return NULL;
         }
+#endif
 
         length = rb_calculate_event_length(length);
  again:
@@ -3498,6 +3500,7 @@ int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
 
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 /**
  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
  * @buffer_a: One buffer to swap with
@@ -3573,6 +3576,7 @@ out:
         return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
+#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
 
 /**
  * ring_buffer_alloc_read_page - allocate a page to read from buffer