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Date:      Sun, 1 Sep 2013 23:02:59 +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: r255136 - in head/sys: fs/nfsclient kern sys
Message-ID:  <201309012302.r81N2xwG055662@svn.freebsd.org>
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Author: rmacklem
Date: Sun Sep  1 23:02:59 2013
New Revision: 255136
URL: http://svnweb.freebsd.org/changeset/base/255136

Log:
  Forced dismounts of NFS mounts can fail when thread(s) are stuck
  waiting for an RPC reply from the server while holding the mount
  point busy (mnt_lockref incremented). This happens because dounmount()
  msleep()s waiting for mnt_lockref to become 0, before calling
  VFS_UNMOUNT(). This patch adds a new VFS operation called VFS_PURGE(),
  which the NFS client implements as purging RPCs in progress. Making
  this call before checking mnt_lockref fixes the problem, by ensuring
  that the VOP_xxx() calls will fail and unbusy the mount point.
  
  Reported by:	sbruno
  Reviewed by:	kib
  MFC after:	2 weeks

Modified:
  head/sys/fs/nfsclient/nfs_clvfsops.c
  head/sys/kern/vfs_mount.c
  head/sys/sys/mount.h

Modified: head/sys/fs/nfsclient/nfs_clvfsops.c
==============================================================================
--- head/sys/fs/nfsclient/nfs_clvfsops.c	Sun Sep  1 22:30:24 2013	(r255135)
+++ head/sys/fs/nfsclient/nfs_clvfsops.c	Sun Sep  1 23:02:59 2013	(r255136)
@@ -120,6 +120,7 @@ static vfs_root_t nfs_root;
 static vfs_statfs_t nfs_statfs;
 static vfs_sync_t nfs_sync;
 static vfs_sysctl_t nfs_sysctl;
+static vfs_purge_t nfs_purge;
 
 /*
  * nfs vfs operations.
@@ -134,6 +135,7 @@ static struct vfsops nfs_vfsops = {
 	.vfs_uninit =		ncl_uninit,
 	.vfs_unmount =		nfs_unmount,
 	.vfs_sysctl =		nfs_sysctl,
+	.vfs_purge =		nfs_purge,
 };
 VFS_SET(nfs_vfsops, nfs, VFCF_NETWORK | VFCF_SBDRY);
 
@@ -1676,6 +1678,19 @@ nfs_sysctl(struct mount *mp, fsctlop_t o
 }
 
 /*
+ * Purge any RPCs in progress, so that they will all return errors.
+ * This allows dounmount() to continue as far as VFS_UNMOUNT() for a
+ * forced dismount.
+ */
+static void
+nfs_purge(struct mount *mp)
+{
+	struct nfsmount *nmp = VFSTONFS(mp);
+
+	newnfs_nmcancelreqs(nmp);
+}
+
+/*
  * Extract the information needed by the nlm from the nfs vnode.
  */
 static void

Modified: head/sys/kern/vfs_mount.c
==============================================================================
--- head/sys/kern/vfs_mount.c	Sun Sep  1 22:30:24 2013	(r255135)
+++ head/sys/kern/vfs_mount.c	Sun Sep  1 23:02:59 2013	(r255136)
@@ -1269,8 +1269,16 @@ dounmount(mp, flags, td)
 	}
 	mp->mnt_kern_flag |= MNTK_UNMOUNT | MNTK_NOINSMNTQ;
 	/* Allow filesystems to detect that a forced unmount is in progress. */
-	if (flags & MNT_FORCE)
+	if (flags & MNT_FORCE) {
 		mp->mnt_kern_flag |= MNTK_UNMOUNTF;
+		MNT_IUNLOCK(mp);
+		/*
+		 * Must be done after setting MNTK_UNMOUNTF and before
+		 * waiting for mnt_lockref to become 0.
+		 */
+		VFS_PURGE(mp);
+		MNT_ILOCK(mp);
+	}
 	error = 0;
 	if (mp->mnt_lockref) {
 		mp->mnt_kern_flag |= MNTK_DRAINING;

Modified: head/sys/sys/mount.h
==============================================================================
--- head/sys/sys/mount.h	Sun Sep  1 22:30:24 2013	(r255135)
+++ head/sys/sys/mount.h	Sun Sep  1 23:02:59 2013	(r255136)
@@ -609,6 +609,7 @@ typedef int vfs_sysctl_t(struct mount *m
 		    struct sysctl_req *req);
 typedef void vfs_susp_clean_t(struct mount *mp);
 typedef void vfs_notify_lowervp_t(struct mount *mp, struct vnode *lowervp);
+typedef void vfs_purge_t(struct mount *mp);
 
 struct vfsops {
 	vfs_mount_t		*vfs_mount;
@@ -628,6 +629,7 @@ struct vfsops {
 	vfs_susp_clean_t	*vfs_susp_clean;
 	vfs_notify_lowervp_t	*vfs_reclaim_lowervp;
 	vfs_notify_lowervp_t	*vfs_unlink_lowervp;
+	vfs_purge_t		*vfs_purge;
 	vfs_mount_t		*vfs_spare[6];	/* spares for ABI compat */
 };
 
@@ -757,6 +759,14 @@ vfs_statfs_t	__vfs_statfs;
 	}								\
 } while (0)
 
+#define	VFS_PURGE(MP) do {						\
+	if (*(MP)->mnt_op->vfs_purge != NULL) {				\
+		VFS_PROLOGUE(MP);					\
+		(*(MP)->mnt_op->vfs_purge)(MP);				\
+		VFS_EPILOGUE(MP);					\
+	}								\
+} while (0)
+
 #define VFS_KNOTE_LOCKED(vp, hint) do					\
 {									\
 	if (((vp)->v_vflag & VV_NOKNOTE) == 0)				\

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