X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=src%2Fcommon%2Fconsumer-timer.c;h=a7f4536a25883cde8bec0aa8f4a3d9a13196e379;hb=ec6ea7d01adc8a9d1481ba645b282c92ec27208e;hp=f9c41c0eb0f8f9f32def26028f743ce7df45d322;hpb=2b8f875486548c9d54d62ae465e2fb23c7023d2c;p=lttng-tools.git

diff --git a/src/common/consumer-timer.c b/src/common/consumer-timer.c
index f9c41c0eb..a7f4536a2 100644
--- a/src/common/consumer-timer.c
+++ b/src/common/consumer-timer.c
@@ -56,6 +56,10 @@ static void setmask(sigset_t *mask)
 
 /*
  * Execute action on a timer switch.
+ *
+ * Beware: metadata_switch_timer() should *never* take a mutex also held
+ * while consumer_timer_switch_stop() is called. It would result in
+ * deadlocks.
  */
 static void metadata_switch_timer(struct lttng_consumer_local_data *ctx,
 		int sig, siginfo_t *si, void *uc)
@@ -74,6 +78,20 @@ static void metadata_switch_timer(struct lttng_consumer_local_data *ctx,
 	switch (ctx->type) {
 	case LTTNG_CONSUMER32_UST:
 	case LTTNG_CONSUMER64_UST:
+		/*
+		 * Locks taken by lttng_ustconsumer_request_metadata():
+		 * - metadata_socket_lock
+		 *   - Calling lttng_ustconsumer_recv_metadata():
+		 *     - channel->metadata_cache->lock
+		 *     - Calling consumer_metadata_cache_flushed():
+		 *       - consumer_data.lock
+		 *         - channel->lock
+		 *           - channel->metadata_cache->lock
+		 *
+		 * Both consumer_data.lock and channel->lock currently
+		 * cause a deadlock, since they are held while
+		 * consumer_timer_switch_stop() is called.
+		 */
 		ret = lttng_ustconsumer_request_metadata(ctx, channel);
 		if (ret < 0) {
 			channel->switch_timer_error = 1;