From 91a1929f0722140afa9872423c9d07aa19b5fb0a Mon Sep 17 00:00:00 2001
From: Attilio Rao <attilio@FreeBSD.org>
Date: Wed, 6 Jul 2011 15:09:52 +0000
Subject: [PATCH] Handle a race between device_pager and devsw in a more
 graceful manner: return an error code rather than panic the kernel.

Sponsored by:	Sandvine Incorporated
Reviewed by:	kib
Tested by:	pho
MFC after:	2 weeks
---
 sys/vm/device_pager.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/sys/vm/device_pager.c b/sys/vm/device_pager.c
index f2131dd29f49..411482a3cc25 100644
--- a/sys/vm/device_pager.c
+++ b/sys/vm/device_pager.c
@@ -217,8 +217,10 @@ dev_pager_getpages(object, m, count, reqpage)
 	memattr = object->memattr;
 	VM_OBJECT_UNLOCK(object);
 	csw = dev_refthread(dev, &ref);
-	if (csw == NULL)
-		panic("dev_pager_getpage: no cdevsw");
+	if (csw == NULL) {
+		VM_OBJECT_LOCK(object);
+		return (VM_PAGER_FAIL);
+	}
 	td = curthread;
 	fpop = td->td_fpop;
 	td->td_fpop = NULL;