ring-buffer: add locks around rb_per_cpu_empty

The checking of whether the buffer is empty or not needs to be serialized
among the readers. Add the reader spin lock around it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2e99dba6dc48..969f7cbe8e93 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2756,12 +2756,17 @@ EXPORT_SYMBOL_GPL(ring_buffer_reset);
 int ring_buffer_empty(struct ring_buffer *buffer)
 {
         struct ring_buffer_per_cpu *cpu_buffer;
+        unsigned long flags;
         int cpu;
+        int ret;
 
         /* yes this is racy, but if you don't like the race, lock the buffer */
         for_each_buffer_cpu(buffer, cpu) {
                 cpu_buffer = buffer->buffers[cpu];
-                if (!rb_per_cpu_empty(cpu_buffer))
+                spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+                ret = rb_per_cpu_empty(cpu_buffer);
+                spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+                if (!ret)
                         return 0;
         }
 
@@ -2777,14 +2782,16 @@ EXPORT_SYMBOL_GPL(ring_buffer_empty);
 int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
 {
         struct ring_buffer_per_cpu *cpu_buffer;
+        unsigned long flags;
         int ret;
 
         if (!cpumask_test_cpu(cpu, buffer->cpumask))
                 return 1;
 
         cpu_buffer = buffer->buffers[cpu];
+        spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
         ret = rb_per_cpu_empty(cpu_buffer);
-
+        spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
         return ret;
 }