Fix for out of order device destruction notifications when using the

delist_dev() function. In addition to this change:
- add a proper description of this function
- add a proper witness assert inside this function
- switch a nearby line to use the "cdp" pointer instead of cdev2priv()

MFC after:	3 days

1 files changed, 18 insertions, 2 deletions

diff --git a/sys/kern/kern_conf.c b/sys/kern/kern_conf.c
index 79c8fea..2056542 100644
--- a/sys/kern/kern_conf.c
+++ b/sys/kern/kern_conf.c
@@ -1093,9 +1093,12 @@ destroy_devl(struct cdev *dev)
 	}
 
 	dev_unlock();
-	notify_destroy(dev);
+	if ((cdp->cdp_flags & CDP_UNREF_DTR) == 0) {
+		/* avoid out of order notify events */
+		notify_destroy(dev);
+	}
 	mtx_lock(&cdevpriv_mtx);
-	while ((p = LIST_FIRST(&cdev2priv(dev)->cdp_fdpriv)) != NULL) {
+	while ((p = LIST_FIRST(&cdp->cdp_fdpriv)) != NULL) {
 		devfs_destroy_cdevpriv(p);
 		mtx_lock(&cdevpriv_mtx);
 	}
@@ -1141,12 +1144,25 @@ delist_dev_locked(struct cdev *dev)
 	devfs_destroy(dev);
 	LIST_FOREACH(child, &dev->si_children, si_siblings)
 		delist_dev_locked(child);
+	dev_unlock();	
+	/* ensure the destroy event is queued in order */
+	notify_destroy(dev);
+	dev_lock();
 }
 
+/*
+ * This function will delist a character device and its children from
+ * the directory listing and create a destroy event without waiting
+ * for all character device references to go away. At some later point
+ * destroy_dev() must be called to complete the character device
+ * destruction. After calling this function the character device name
+ * can instantly be re-used.
+ */
 void
 delist_dev(struct cdev *dev)
 {
 
+	WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "delist_dev");
 	dev_lock();
 	delist_dev_locked(dev);
 	dev_unlock();