Fix a LOR in the NFS client which could cause a deadlock.

This was reported to the mailing list freebsd-net@freebsd.org
on July 21, 2011 under the subject "LOR with nfsclient sillyrename".
The LOR occurred when nfs_inactive() called vrele(sp->s_dvp)
while holding the vnode lock on the file in s_dvp. This patch
modifies the client so that it performs the vrele(sp->s_dvp)
as a separate task to avoid the LOR. This fix was discussed
with jhb@ and kib@, who both proposed variations of it.

Tested by:	pho, jlott at averesystems.com
Submitted by:	jhb (earlier version)
Reviewed by:	kib
Approved by:	re (kib)
MFC after:	2 weeks

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/fs/nfsclient/nfsnode.h b/sys/fs/nfsclient/nfsnode.h
index 1d1c89c..c29805d 100644
--- a/sys/fs/nfsclient/nfsnode.h
+++ b/sys/fs/nfsclient/nfsnode.h
@@ -35,11 +35,14 @@
 #ifndef _NFSCLIENT_NFSNODE_H_
 #define	_NFSCLIENT_NFSNODE_H_
 
+#include <sys/_task.h>
+
 /*
  * Silly rename structure that hangs off the nfsnode until the name
  * can be removed by nfs_inactive()
  */
 struct sillyrename {
+	struct	task s_task;
 	struct	ucred *s_cred;
 	struct	vnode *s_dvp;
 	long	s_namlen;