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From: Attilio Rao <attilio@FreeBSD.org>
Date: Wed, 6 Jul 2011 15:09:52 +0000 (UTC)
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Subject: svn commit: r223823 - head/sys/vm
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Author: attilio
Date: Wed Jul  6 15:09:52 2011
New Revision: 223823
URL: http://svn.freebsd.org/changeset/base/223823

Log:
  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

Modified:
  head/sys/vm/device_pager.c

Modified: head/sys/vm/device_pager.c
==============================================================================
--- head/sys/vm/device_pager.c	Wed Jul  6 09:43:25 2011	(r223822)
+++ head/sys/vm/device_pager.c	Wed Jul  6 15:09:52 2011	(r223823)
@@ -217,8 +217,10 @@ dev_pager_getpages(object, m, count, req
 	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;