MAJOR: threads/buffer: Make buffer wait queue thread safe

Adds a global lock to protect the buffer wait queue.
diff --git a/include/common/buffer.h b/include/common/buffer.h
index 17931cf..f11d6a9 100644
--- a/include/common/buffer.h
+++ b/include/common/buffer.h
@@ -52,6 +52,9 @@
 extern struct buffer buf_empty;
 extern struct buffer buf_wanted;
 extern struct list buffer_wq;
+#ifdef USE_THREAD
+extern HA_SPINLOCK_T buffer_wq_lock;
+#endif
 
 int init_buffer();
 void deinit_buffer();
@@ -748,9 +751,13 @@
 
 static inline void offer_buffers(void *from, unsigned int threshold)
 {
-	if (LIST_ISEMPTY(&buffer_wq))
+	SPIN_LOCK(BUF_WQ_LOCK, &buffer_wq_lock);
+	if (LIST_ISEMPTY(&buffer_wq)) {
+		SPIN_UNLOCK(BUF_WQ_LOCK, &buffer_wq_lock);
 		return;
+	}
 	__offer_buffer(from, threshold);
+	SPIN_UNLOCK(BUF_WQ_LOCK, &buffer_wq_lock);
 }
 
 /*************************************************************************/
diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 3a77bd1..1717cc9 100644
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -156,6 +156,7 @@
 	STK_SESS_LOCK,
 	APPLETS_LOCK,
 	PEER_LOCK,
+	BUF_WQ_LOCK,
 	LOCK_LABELS
 };
 struct lock_stat {
@@ -242,7 +243,7 @@
 					   "TASK_RQ", "TASK_WQ", "POOL",
 					   "LISTENER", "LISTENER_QUEUE", "PROXY", "SERVER",
 					   "UPDATED_SERVERS", "LBPRM", "SIGNALS", "STK_TABLE", "STK_SESS",
-					   "APPLETS", "PEER" };
+					   "APPLETS", "PEER", "BUF_WQ" };
 	int lbl;
 
 	for (lbl = 0; lbl < LOCK_LABELS; lbl++) {
diff --git a/include/proto/applet.h b/include/proto/applet.h
index d9f0ce2..766fc92 100644
--- a/include/proto/applet.h
+++ b/include/proto/applet.h
@@ -88,8 +88,10 @@
 	}
 
 	if (!LIST_ISEMPTY(&appctx->buffer_wait.list)) {
+		SPIN_LOCK(BUF_WQ_LOCK, &buffer_wq_lock);
 		LIST_DEL(&appctx->buffer_wait.list);
 		LIST_INIT(&appctx->buffer_wait.list);
+		SPIN_UNLOCK(BUF_WQ_LOCK, &buffer_wq_lock);
 	}
 
 	pool_free2(pool2_connection, appctx);
diff --git a/include/proto/channel.h b/include/proto/channel.h
index 9e12b5e..83ad0aa 100644
--- a/include/proto/channel.h
+++ b/include/proto/channel.h
@@ -440,8 +440,12 @@
 	if (b_alloc_margin(&chn->buf, margin) != NULL)
 		return 1;
 
-	if (LIST_ISEMPTY(&wait->list))
+	if (LIST_ISEMPTY(&wait->list)) {
+		SPIN_LOCK(BUF_WQ_LOCK, &buffer_wq_lock);
 		LIST_ADDQ(&buffer_wq, &wait->list);
+		SPIN_UNLOCK(BUF_WQ_LOCK, &buffer_wq_lock);
+	}
+
 	return 0;
 }