tracing: Do not risk busy looping in buffer splice

If the read loop in trace_buffers_splice_read() keeps failing due to
memory allocation failures without reading even a single page then this
function will keep busy looping.

Remove the risk for that by exiting the function if memory allocation
failures are seen.

Link: http://lkml.kernel.org/r/1415309167-2373-2-git-send-email-rabin@rab.in

Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -5494,7 +5494,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 	};
 	struct buffer_ref *ref;
 	int entries, size, i;
-	ssize_t ret;
+	ssize_t ret = 0;
 
 	mutex_lock(&trace_types_lock);
 
@@ -5532,13 +5532,16 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 		int r;
 
 		ref = kzalloc(sizeof(*ref), GFP_KERNEL);
-		if (!ref)
+		if (!ref) {
+			ret = -ENOMEM;
 			break;
+		}
 
 		ref->ref = 1;
 		ref->buffer = iter->trace_buffer->buffer;
 		ref->page = ring_buffer_alloc_read_page(ref->buffer, iter->cpu_file);
 		if (!ref->page) {
+			ret = -ENOMEM;
 			kfree(ref);
 			break;
 		}
@@ -5576,6 +5579,9 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 
 	/* did we read anything? */
 	if (!spd.nr_pages) {
+		if (ret)
+			goto out;
+
 		if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK)) {
 			ret = -EAGAIN;
 			goto out;