Revert "Cleanup: ring buffer: remove lib_ring_buffer_switch_new_end()"

[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 2626afa31e3ea9f33a7e9ebbab98bd91d510b723..77f9e8bb4f560591f025d5b2b30b07fa4e1a777d 100644 (file)
--- 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)
 {
@@ -927,6 +927,13 @@ int lib_ring_buffer_get_subbuf(struct lib_ring_buffer *buf,
        int ret;
        int finalized;
 
+       if (buf->get_subbuf) {
+               /*
+                * Reader is trying to get a subbuffer twice.
+                */
+               CHAN_WARN_ON(chan, 1);
+               return -EBUSY;
+       }
 retry:
        finalized = ACCESS_ONCE(buf->finalized);
        /*
@@ -1516,6 +1523,48 @@ 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