Fix: ring buffer: RING_BUFFER_FLUSH ioctl buffer corruption

[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..942e14d3b9023d9ce76f797a834812329542b634 100644 (file)
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1516,6 +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