X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=lib%2Fringbuffer%2Fring_buffer_frontend.c;h=92aa78f57ddf2ed95f42c16e23728d32f58291b6;hb=294d35794ac83c4321e4bd3d56317844771517ae;hp=dc0357f56a3e71547c7da80a4e2bd3ce7277d0f0;hpb=886d51a3d7ed5fa6b41d7f19b3e14ae6c535a44c;p=lttng-modules.git

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index dc0357f5..92aa78f5 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -402,7 +402,7 @@ static void lib_ring_buffer_stop_read_timer(struct lib_ring_buffer *buf)
  *	Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
  */
 static
-int __cpuinit lib_ring_buffer_cpu_hp_callback(struct notifier_block *nb,
+int lib_ring_buffer_cpu_hp_callback(struct notifier_block *nb,
 					      unsigned long action,
 					      void *hcpu)
 {
@@ -1424,6 +1424,19 @@ int lib_ring_buffer_try_switch_slow(enum switch_mode mode,
 	 */
 	if (mode == SWITCH_FLUSH || off > 0) {
 		if (unlikely(off == 0)) {
+                        /*
+			 * A final flush that encounters an empty
+			 * sub-buffer cannot switch buffer if a
+			 * reader is located within this sub-buffer.
+			 * Anyway, the purpose of final flushing of a
+			 * sub-buffer at offset 0 is to handle the case
+			 * of entirely empty stream.
+			 */
+			if (unlikely(subbuf_trunc(offsets->begin, chan)
+					- subbuf_trunc((unsigned long)
+						atomic_long_read(&buf->consumed), chan)
+					>= chan->backend.buf_size))
+				return -1;
 			/*
 			 * The client does not save any header information.
 			 * Don't switch empty subbuffer on finalize, because it
@@ -1503,6 +1516,48 @@ void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf, enum switch_mode m
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow);
 
+static void remote_switch(void *info)
+{
+	struct lib_ring_buffer *buf = info;
+
+	lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+}
+
+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;
+
+	/*
+	 * With global synchronization we don't need to use the IPI scheme.
+	 */
+	if (config->sync == RING_BUFFER_SYNC_GLOBAL) {
+		lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+		return;
+	}
+
+	/*
+	 * Taking lock on CPU hotplug to ensure two things: first, that the
+	 * target cpu is not taken concurrently offline while we are within
+	 * smp_call_function_single() (I don't trust that get_cpu() on the
+	 * _local_ CPU actually inhibit CPU hotplug for the _remote_ CPU (to be
+	 * confirmed)). Secondly, if it happens that the CPU is not online, our
+	 * own call to lib_ring_buffer_switch_slow() needs to be protected from
+	 * CPU hotplug handlers, which can also perform a remote subbuffer
+	 * switch.
+	 */
+	get_online_cpus();
+	ret = smp_call_function_single(buf->backend.cpu,
+				 remote_switch, buf, 1);
+	if (ret) {
+		/* Remote CPU is offline, do it ourself. */
+		lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+	}
+	put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote);
+
 /*
  * Returns :
  * 0 if ok