[syslog-ng] [PATCH 1/1] afmongodb: Fix a race condition in the queue & wakeup mechanism

[Gergely Nagy]

The problem was found and analysed by Whille, the patch is based on
his observations.

The patch corrects a situation where - due to a race condition - the
worker thread could end up in a permanent sleeping state.

Reported-by: whille <whille at 163.com>
Signed-off-by: Gergely Nagy <algernon at balabit.hu>
---
 modules/afmongodb/afmongodb.c |   18 ++++++------------
 1 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/modules/afmongodb/afmongodb.c b/modules/afmongodb/afmongodb.c
index 42c140e..47b6c9d 100644
--- a/modules/afmongodb/afmongodb.c
+++ b/modules/afmongodb/afmongodb.c
@@ -515,27 +515,21 @@ static void
 afmongodb_dd_queue(LogPipe *s, LogMessage *msg, const LogPathOptions *path_options, gpointer user_data)
 {
   MongoDBDestDriver *self = (MongoDBDestDriver *)s;
-  gboolean queue_was_empty;
   LogPathOptions local_options;
 
   if (!path_options->flow_control_requested)
     path_options = log_msg_break_ack(msg, path_options, &local_options);
 
-  g_mutex_lock(self->queue_mutex);
   self->last_msg_stamp = cached_g_current_time_sec ();
-  queue_was_empty = log_queue_get_length(self->queue) == 0;
-  g_mutex_unlock(self->queue_mutex);
-  
-  log_queue_push_tail(self->queue, msg, path_options);
 
   g_mutex_lock(self->suspend_mutex);
-  if (queue_was_empty && !self->writer_thread_suspended)
-    {
-      g_mutex_lock(self->queue_mutex);
-      log_queue_set_parallel_push(self->queue, 1, afmongodb_dd_queue_notify, self, NULL);
-      g_mutex_unlock(self->queue_mutex);
-    }
+  g_mutex_lock(self->queue_mutex);
+  if (!self->writer_thread_suspended)
+    log_queue_set_parallel_push(self->queue, 1, afmongodb_dd_queue_notify,
+                                self, NULL);
+  g_mutex_unlock(self->queue_mutex);
   g_mutex_unlock(self->suspend_mutex);
+  log_queue_push_tail(self->queue, msg, path_options);
 }
 
 /*
-- 
1.7.9