From dcf26f79144e1b9056a0cdbaa9b570239c8080b2 Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@dragonflybsd.org>
Date: Tue, 19 Sep 2006 18:17:46 +0000
Subject: [PATCH] Check that namecache references to the mount point are no
 longer present before unmounting a filesystem.  Forced unmounts ignore the
 check but will print a warning.

This patch is primarily designed to prevent nullfs partitions from being
unmounted while processes are still present within them.  The normal vnode
check does not work for nullfs mounts since nullfs mounts do not hold any
vnodes of their own.

Note that this will cause a warning to be reported for the root filesystem
when rebooting.
---
 sys/kern/vfs_syscalls.c | 54 ++++++++++++++++++++++++++++++++---------
 1 file changed, 43 insertions(+), 11 deletions(-)

diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 2a360085fc..6b7a56475c 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -37,7 +37,7 @@
  *
  *	@(#)vfs_syscalls.c	8.13 (Berkeley) 4/15/94
  * $FreeBSD: src/sys/kern/vfs_syscalls.c,v 1.151.2.18 2003/04/04 20:35:58 tegge Exp $
- * $DragonFly: src/sys/kern/vfs_syscalls.c,v 1.105 2006/09/19 16:06:11 dillon Exp $
+ * $DragonFly: src/sys/kern/vfs_syscalls.c,v 1.106 2006/09/19 18:17:46 dillon Exp $
  */
 
 #include <sys/param.h>
@@ -570,6 +570,7 @@ dounmount_interlock(struct mount *mp)
 int
 dounmount(struct mount *mp, int flags)
 {
+	struct namecache *ncp;
 	int error;
 	int async_flag;
 	int lflags;
@@ -600,13 +601,44 @@ dounmount(struct mount *mp, int flags)
 	vfs_msync(mp, MNT_WAIT);
 	async_flag = mp->mnt_flag & MNT_ASYNC;
 	mp->mnt_flag &=~ MNT_ASYNC;
-	cache_purgevfs(mp);	/* remove cache entries for this file sys */
-	if (mp->mnt_syncer != NULL)
-		vrele(mp->mnt_syncer);
-	if (((mp->mnt_flag & MNT_RDONLY) ||
-	     (error = VFS_SYNC(mp, MNT_WAIT)) == 0) ||
-	    (flags & MNT_FORCE))
-		error = VFS_UNMOUNT(mp, flags);
+
+	/*
+	 * remove cache entries for this file sys and determine if anyone
+	 * other then us is still holding onto any namecache references.
+	 *
+	 * XXX need separate ref counter on mount structure to delay
+	 * kfree()ing it.
+	 */
+	cache_purgevfs(mp);
+	if ((ncp = mp->mnt_ncp) != NULL) {
+		if (ncp->nc_refs != 1 || TAILQ_FIRST(&ncp->nc_list)) {
+			char *ptr;
+			char *buf;
+
+			if ((flags & MNT_FORCE) == 0) {
+				error = EBUSY;
+			} else if (cache_fullpath(NULL, ncp, &ptr, &buf)) {
+				printf("Warning: forced unmount - "
+				       "namecache references still present\n");
+			} else {
+				printf("Warning: forced unmount of %s - "
+				       "namecache references still present\n",
+				       ptr
+				);
+				kfree(buf, M_TEMP);
+			}
+		}
+	}
+
+	if (error == 0) {
+		if (mp->mnt_syncer != NULL)
+			vrele(mp->mnt_syncer);
+		if (((mp->mnt_flag & MNT_RDONLY) ||
+		     (error = VFS_SYNC(mp, MNT_WAIT)) == 0) ||
+		    (flags & MNT_FORCE)) {
+			error = VFS_UNMOUNT(mp, flags);
+		}
+	}
 	if (error) {
 		if (mp->mnt_syncer == NULL)
 			vfs_allocate_syncvnode(mp);
@@ -636,9 +668,9 @@ dounmount(struct mount *mp, int flags)
 	vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_spec_ops);
 	vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_fifo_ops);
 
-	if (mp->mnt_ncp) {
-		cache_clrmountpt(mp->mnt_ncp);
-		cache_drop(mp->mnt_ncp);
+	if ((ncp = mp->mnt_ncp) != NULL) {
+		cache_clrmountpt(ncp);
+		cache_drop(ncp);
 		mp->mnt_ncp = NULL;
 	}
 
-- 
2.41.0