From 3a54ca5e28d847ab46168d3ea866259e806338fe Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Mon, 10 Mar 2025 13:32:23 -0400
Subject: [PATCH] new-bus: Add taskqueue_bus to process hot-plug device events

Use a system-wide taskqueue for hot-plug events.  This avoids possibly
blocking unrelated events on the thread taskqueue without requiring
multiple driver-specific taskqueues.

Reviewed by:	imp
Differential Revision:	https://reviews.freebsd.org/D49268

(cherry picked from commit 44d5f5ed1e959d8f2c22b6ee69c6a46a45ccdd8e)
---
 sys/kern/subr_bus.c | 3 +++
 sys/sys/taskqueue.h | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index b71a46edc54..211fe45b137 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -51,6 +51,7 @@
 #include <sys/smp.h>
 #include <sys/sysctl.h>
 #include <sys/systm.h>
+#include <sys/taskqueue.h>
 #include <sys/bus.h>
 #include <sys/cpuset.h>
 #ifdef INTRNG
@@ -120,6 +121,8 @@ struct device_prop_elm {
 	LIST_ENTRY(device_prop_elm) link;
 };
 
+TASKQUEUE_DEFINE_THREAD(bus);
+
 static void device_destroy_props(device_t dev);
 
 /**
diff --git a/sys/sys/taskqueue.h b/sys/sys/taskqueue.h
index 9757e1fce57..9da364a1a71 100644
--- a/sys/sys/taskqueue.h
+++ b/sys/sys/taskqueue.h
@@ -215,4 +215,10 @@ struct taskqueue *taskqueue_create_fast(const char *name, int mflags,
 				    taskqueue_enqueue_fn enqueue,
 				    void *context);
 
+/*
+ * This queue is used to process asynchronous device events such as
+ * hot plug insertion and removal of devices.
+ */
+TASKQUEUE_DECLARE(bus);
+
 #endif /* !_SYS_TASKQUEUE_H_ */