From: Julien Desfossez <jdesfossez@efficios.com>
Date: Fri, 14 Feb 2014 20:51:34 +0000 (-0500)
Subject: Fix: deadlock during rotation
X-Git-Tag: v2.5.0-rc1~172
X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=commitdiff_plain;h=56611b069e7d0a64148cd990f88b4090298a9a0f

Fix: deadlock during rotation

The overwrite_lock is nested inside the viewer_stream_rotation_lock.
And the viewer_stream_rotate function is always called with the
viewer_stream_rotation_lock held.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
---

diff --git a/src/bin/lttng-relayd/live.c b/src/bin/lttng-relayd/live.c
index d29804cd6..a720ed732 100644
--- a/src/bin/lttng-relayd/live.c
+++ b/src/bin/lttng-relayd/live.c
@@ -1337,11 +1337,13 @@ int viewer_get_next_index(struct relay_connection *conn)
 		viewer_index.flags |= LTTNG_VIEWER_FLAG_NEW_STREAM;
 	}
 
+	pthread_mutex_lock(&rstream->viewer_stream_rotation_lock);
 	pthread_mutex_lock(&vstream->overwrite_lock);
 	if (vstream->abort_flag) {
 		/* The file is being overwritten by the writer, we cannot use it. */
 		pthread_mutex_unlock(&vstream->overwrite_lock);
 		ret = viewer_stream_rotate(vstream, rstream);
+		pthread_mutex_unlock(&rstream->viewer_stream_rotation_lock);
 		if (ret < 0) {
 			goto end_unlock;
 		} else if (ret == 1) {
@@ -1357,6 +1359,7 @@ int viewer_get_next_index(struct relay_connection *conn)
 	read_ret = lttng_read(vstream->index_read_fd, &packet_index,
 			sizeof(packet_index));
 	pthread_mutex_unlock(&vstream->overwrite_lock);
+	pthread_mutex_unlock(&rstream->viewer_stream_rotation_lock);
 	if (read_ret < 0) {
 		viewer_index.status = htobe32(LTTNG_VIEWER_INDEX_HUP);
 		viewer_stream_delete(vstream);
diff --git a/src/bin/lttng-relayd/viewer-stream.c b/src/bin/lttng-relayd/viewer-stream.c
index 8ed84a1d1..5ab7be790 100644
--- a/src/bin/lttng-relayd/viewer-stream.c
+++ b/src/bin/lttng-relayd/viewer-stream.c
@@ -196,6 +196,7 @@ end:
 /*
  * Rotate a stream to the next tracefile.
  *
+ * Must be called with viewer_stream_rotation_lock held.
  * Returns 0 on success, 1 on EOF, a negative value on error.
  */
 int viewer_stream_rotate(struct relay_viewer_stream *vstream,
@@ -224,12 +225,6 @@ int viewer_stream_rotate(struct relay_viewer_stream *vstream,
 		goto end;
 	}
 
-	/*
-	 * Lock to execute rotation in order to avoid races between a modification
-	 * on the index values.
-	 */
-	pthread_mutex_lock(&stream->viewer_stream_rotation_lock);
-
 	/*
 	 * The writer and the reader are not working in the same tracefile, we can
 	 * read up to EOF, we don't care about the total_index_received.
@@ -264,8 +259,6 @@ int viewer_stream_rotate(struct relay_viewer_stream *vstream,
 	vstream->abort_flag = 0;
 	pthread_mutex_unlock(&vstream->overwrite_lock);
 
-	pthread_mutex_unlock(&stream->viewer_stream_rotation_lock);
-
 	ret = index_open(vstream->path_name, vstream->channel_name,
 			vstream->tracefile_count, vstream->tracefile_count_current);
 	if (ret < 0) {