ring-buffer: add locks around rb_per_cpu_empty
Steven Rostedt [Wed, 17 Jun 2009 04:39:43 +0000 (00:39 -0400)]
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>

kernel/trace/ring_buffer.c

index 2e99dba..969f7cb 100644 (file)
@@ -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;
 }