From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Wed, 21 Dec 2016 22:56:24 +0000 (-0500)
Subject: Fix: protect the channel's metadata stream using the metadata cache lock
X-Git-Tag: v2.9.1~2
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=6ba5305c8ec548191f30c9e0c540faeb1977252a;p=lttng-tools.git

Fix: protect the channel's metadata stream using the metadata cache lock

The consumer_thread_data_poll and consumer_thread_metadata_poll
both access the channel's metadata stream.

During a session destruction, consumer_thread_metadata_poll will
destroy all metadata streams. However, the consumer_thread_data_poll
may still invoke a consumer_metadata_cache_write() triggered
by a "ready" subbuffer. Hence, the metadata stream must be protected
from this action by the metadata cache lock.

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

diff --git a/src/common/consumer/consumer-metadata-cache.c b/src/common/consumer/consumer-metadata-cache.c
index 3211ec1e8..6b15375e1 100644
--- a/src/common/consumer/consumer-metadata-cache.c
+++ b/src/common/consumer/consumer-metadata-cache.c
@@ -147,7 +147,7 @@ int consumer_metadata_cache_write(struct lttng_consumer_channel *channel,
 		char dummy = 'c';
 
 		cache->max_offset = offset + len;
-		if (channel->monitor) {
+		if (channel->monitor && channel->metadata_stream) {
 			size_ret = lttng_write(channel->metadata_stream->ust_metadata_poll_pipe[1],
 					&dummy, 1);
 			if (size_ret < 1) {
diff --git a/src/common/consumer/consumer.c b/src/common/consumer/consumer.c
index 929be6553..54a0531d5 100644
--- a/src/common/consumer/consumer.c
+++ b/src/common/consumer/consumer.c
@@ -47,6 +47,7 @@
 #include <common/consumer/consumer-stream.h>
 #include <common/consumer/consumer-testpoint.h>
 #include <common/align.h>
+#include <common/consumer/consumer-metadata-cache.h>
 
 struct lttng_consumer_global_data consumer_data = {
 	.stream_count = 0,
@@ -2051,6 +2052,7 @@ void consumer_del_metadata_stream(struct lttng_consumer_stream *stream,
 
 	pthread_mutex_lock(&consumer_data.lock);
 	pthread_mutex_lock(&stream->chan->lock);
+	pthread_mutex_lock(&stream->chan->metadata_cache->lock);
 	pthread_mutex_lock(&stream->lock);
 
 	/* Remove any reference to that stream. */
@@ -2076,6 +2078,7 @@ void consumer_del_metadata_stream(struct lttng_consumer_stream *stream,
 	stream->chan->metadata_stream = NULL;
 
 	pthread_mutex_unlock(&stream->lock);
+	pthread_mutex_unlock(&stream->chan->metadata_cache->lock);
 	pthread_mutex_unlock(&stream->chan->lock);
 	pthread_mutex_unlock(&consumer_data.lock);