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Date:      Wed, 17 Aug 2011 20:55:56 +0000 (UTC)
From:      Rick Macklem <rmacklem@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org
Subject:   svn commit: r224951 - stable/8/sys/fs/nfsclient
Message-ID:  <201108172055.p7HKtuSC022694@svn.freebsd.org>
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Author: rmacklem
Date: Wed Aug 17 20:55:56 2011
New Revision: 224951
URL: http://svn.freebsd.org/changeset/base/224951

Log:
  MFC: r224606
  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.

Modified:
  stable/8/sys/fs/nfsclient/nfs_clnode.c
  stable/8/sys/fs/nfsclient/nfsnode.h
Directory Properties:
  stable/8/sys/   (props changed)
  stable/8/sys/amd64/include/xen/   (props changed)
  stable/8/sys/cddl/contrib/opensolaris/   (props changed)
  stable/8/sys/contrib/dev/acpica/   (props changed)
  stable/8/sys/contrib/pf/   (props changed)

Modified: stable/8/sys/fs/nfsclient/nfs_clnode.c
==============================================================================
--- stable/8/sys/fs/nfsclient/nfs_clnode.c	Wed Aug 17 20:43:59 2011	(r224950)
+++ stable/8/sys/fs/nfsclient/nfs_clnode.c	Wed Aug 17 20:55:56 2011	(r224951)
@@ -45,6 +45,7 @@ __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>
@@ -62,6 +63,8 @@ MALLOC_DECLARE(M_NEWNFSREQ);
 
 uma_zone_t newnfsnode_zone;
 
+static void	nfs_freesillyrename(void *arg, __unused int pending);
+
 void
 ncl_nhinit(void)
 {
@@ -183,6 +186,20 @@ ncl_nget(struct mount *mntp, u_int8_t *f
 	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_NEWNFSREQ);
+}
+
 int
 ncl_inactive(struct vop_inactive_args *ap)
 {
@@ -217,8 +234,8 @@ ncl_inactive(struct vop_inactive_args *a
 		 */
 		ncl_removeit(sp, vp);
 		crfree(sp->s_cred);
-		vrele(sp->s_dvp);
-		FREE((caddr_t)sp, M_NEWNFSREQ);
+		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: stable/8/sys/fs/nfsclient/nfsnode.h
==============================================================================
--- stable/8/sys/fs/nfsclient/nfsnode.h	Wed Aug 17 20:43:59 2011	(r224950)
+++ stable/8/sys/fs/nfsclient/nfsnode.h	Wed Aug 17 20:55:56 2011	(r224951)
@@ -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;

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