Fix: ring buffer: honor switch parameter type in remote switch

[lttng-modules.git] / lib / ringbuffer / ring_buffer_frontend.c

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index c48ac620668f97f3ea7f3ff1222c16f62a40add9..379bf95e67799c6bfee928c63e2636478a984b3f 100644 (file)
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1293,7 +1293,8 @@ void lib_ring_buffer_print_errors(struct channel *chan,
 /*
  * lib_ring_buffer_switch_old_start: Populate old subbuffer header.
  *
- * Only executed when the buffer is finalized, in SWITCH_FLUSH.
+ * Only executed by SWITCH_FLUSH, which can be issued while tracing is active
+ * or at buffer finalization (destroy).
  */
 static
 void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
@@ -1484,12 +1485,14 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode,
                unsigned long sb_index, commit_count;
 
                /*
-                * We are performing a SWITCH_FLUSH. At this stage, there are no
-                * concurrent writes into the buffer.
+                * We are performing a SWITCH_FLUSH. There may be concurrent
+                * writes into the buffer if e.g. invoked while performing a
+                * snapshot on an active trace.
                 *
-                * The client does not save any header information.  Don't
-                * switch empty subbuffer on finalize, because it is invalid to
-                * deliver a completely empty subbuffer.
+                * If the client does not save any header information (sub-buffer
+                * header size == 0), don't switch empty subbuffer on finalize,
+                * because it is invalid to deliver a completely empty
+                * subbuffer.
                 */
                if (!config->cb.subbuffer_header_size())
                        return -1;
@@ -1603,11 +1606,17 @@ void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf, enum switch_mode m
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow);
 
+struct switch_param {
+       struct lib_ring_buffer *buf;
+       enum switch_mode mode;
+};
+
 static void remote_switch(void *info)
 {
-       struct lib_ring_buffer *buf = info;
+       struct switch_param *param = info;
+       struct lib_ring_buffer *buf = param->buf;
 
-       lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+       lib_ring_buffer_switch_slow(buf, param->mode);
 }
 
 static void _lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf,
@@ -1616,6 +1625,7 @@ static void _lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf,
        struct channel *chan = buf->backend.chan;
        const struct lib_ring_buffer_config *config = &chan->backend.config;
        int ret;
+       struct switch_param param;
 
        /*
         * With global synchronization we don't need to use the IPI scheme.
@@ -1636,8 +1646,10 @@ static void _lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf,
         * switch.
         */
        get_online_cpus();
+       param.buf = buf;
+       param.mode = mode;
        ret = smp_call_function_single(buf->backend.cpu,
-                                remote_switch, buf, 1);
+                                remote_switch, &param, 1);
        if (ret) {
                /* Remote CPU is offline, do it ourself. */
                lib_ring_buffer_switch_slow(buf, mode);
@@ -1651,6 +1663,13 @@ void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf)
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote);
 
+/* Switch sub-buffer even if current sub-buffer is empty. */
+void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer *buf)
+{
+       _lib_ring_buffer_switch_remote(buf, SWITCH_FLUSH);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote_empty);
+
 /*
  * Returns :
  * 0 if ok