From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Sat, 7 Jan 2017 18:42:12 +0000 (-0500)
Subject: Fix: only lock the metadata_cache in userspace consumers
X-Git-Tag: v2.8.5~1
X-Git-Url: https://git.liburcu.org/?p=lttng-tools.git;a=commitdiff_plain;h=4486a5729f7938cd4aa4c936c8cd8ba71f69534e

Fix: only lock the metadata_cache in userspace consumers

The kernel consumer, which re-uses the consumer_del_metadata_stream
function, has no metadata cache. Therefore, it can't be used to
protect the metadata stream (see 5feafd41).

However, only the userspace consumers invoke
consumer_metadata_cache_write() which the previous fix seeked to
protect against. It is therefore safe to omit this lock in the
kernel consumer case.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/common/consumer/consumer.c b/src/common/consumer/consumer.c
index 21adb00b4..19d705c93 100644
--- a/src/common/consumer/consumer.c
+++ b/src/common/consumer/consumer.c
@@ -2052,7 +2052,10 @@ void consumer_del_metadata_stream(struct lttng_consumer_stream *stream,
 	DBG3("Consumer delete metadata stream %d", stream->wait_fd);
 
 	pthread_mutex_lock(&consumer_data.lock);
-	pthread_mutex_lock(&stream->chan->metadata_cache->lock);
+	if (stream->chan->metadata_cache) {
+		/* Only applicable to userspace consumers. */
+		pthread_mutex_lock(&stream->chan->metadata_cache->lock);
+	}
 	pthread_mutex_lock(&stream->chan->lock);
 	pthread_mutex_lock(&stream->lock);
 
@@ -2080,7 +2083,9 @@ void consumer_del_metadata_stream(struct lttng_consumer_stream *stream,
 
 	pthread_mutex_unlock(&stream->lock);
 	pthread_mutex_unlock(&stream->chan->lock);
-	pthread_mutex_unlock(&stream->chan->metadata_cache->lock);
+	if (stream->chan->metadata_cache) {
+		pthread_mutex_unlock(&stream->chan->metadata_cache->lock);
+	}
 	pthread_mutex_unlock(&consumer_data.lock);
 
 	if (free_chan) {