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Date:      Tue, 2 Aug 2011 11:24:42 +0000 (UTC)
From:      Rick Macklem <rmacklem@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r224604 - head/sys/nfsclient
Message-ID:  <201108021124.p72BOgEU047930@svn.freebsd.org>
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Author: rmacklem
Date: Tue Aug  2 11:24:42 2011
New Revision: 224604
URL: http://svn.freebsd.org/changeset/base/224604

Log:
  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

Modified:
  head/sys/nfsclient/nfs_node.c
  head/sys/nfsclient/nfsnode.h

Modified: head/sys/nfsclient/nfs_node.c
==============================================================================
--- head/sys/nfsclient/nfs_node.c	Tue Aug  2 11:07:47 2011	(r224603)
+++ head/sys/nfsclient/nfs_node.c	Tue Aug  2 11:24:42 2011	(r224604)
@@ -47,6 +47,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/proc.h>
 #include <sys/socket.h>
 #include <sys/sysctl.h>
+#include <sys/taskqueue.h>
 #include <sys/vnode.h>
 
 #include <vm/uma.h>
@@ -59,6 +60,8 @@ __FBSDID("$FreeBSD$");
 
 static uma_zone_t nfsnode_zone;
 
+static void	nfs_freesillyrename(void *arg, __unused int pending);
+
 #define TRUE	1
 #define	FALSE	0
 
@@ -185,6 +188,20 @@ nfs_nget(struct mount *mntp, nfsfh_t *fh
 	return (0);
 }
 
+/*
+ * Do the vrele(sp->s_dvp) as a separate task in order to avoid a
+ * deadlock because of a LOR when vrele() locks the directory vnode.
+ */
+static void
+nfs_freesillyrename(void *arg, __unused int pending)
+{
+	struct sillyrename *sp;
+
+	sp = arg;
+	vrele(sp->s_dvp);
+	free(sp, M_NFSREQ);
+}
+
 int
 nfs_inactive(struct vop_inactive_args *ap)
 {
@@ -207,8 +224,8 @@ nfs_inactive(struct vop_inactive_args *a
 		 */
 		(sp->s_removeit)(sp);
 		crfree(sp->s_cred);
-		vrele(sp->s_dvp);
-		free((caddr_t)sp, M_NFSREQ);
+		TASK_INIT(&sp->s_task, 0, nfs_freesillyrename, sp);
+		taskqueue_enqueue(taskqueue_thread, &sp->s_task);
 		mtx_lock(&np->n_mtx);
 	}
 	np->n_flag &= NMODIFIED;

Modified: head/sys/nfsclient/nfsnode.h
==============================================================================
--- head/sys/nfsclient/nfsnode.h	Tue Aug  2 11:07:47 2011	(r224603)
+++ head/sys/nfsclient/nfsnode.h	Tue Aug  2 11:24:42 2011	(r224604)
@@ -36,6 +36,7 @@
 #ifndef _NFSCLIENT_NFSNODE_H_
 #define _NFSCLIENT_NFSNODE_H_
 
+#include <sys/_task.h>
 #if !defined(_NFSCLIENT_NFS_H_) && !defined(_KERNEL)
 #include <nfs/nfs.h>
 #endif
@@ -45,6 +46,7 @@
  * can be removed by nfs_inactive()
  */
 struct sillyrename {
+	struct	task s_task;
 	struct	ucred *s_cred;
 	struct	vnode *s_dvp;
 	int	(*s_removeit)(struct sillyrename *sp);

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