autofs4: correct offset mount expire check

When checking a directory tree in autofs_tree_busy() we can incorrectly
decide that the tree isn't busy.  This happens for the case of an active
offset mount as autofs4_follow_mount() follows past the active offset
mount, which has an open file handle used for expires, causing the file
handle not to count toward the busyness check.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 4 deletions

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index cde2f8e8935a..4b6fb3f628c0 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -56,12 +56,23 @@ static int autofs4_mount_busy(struct vfsmount *mnt, struct dentry *dentry)
         mntget(mnt);
         dget(dentry);
 
-        if (!autofs4_follow_mount(&mnt, &dentry))
+        if (!follow_down(&mnt, &dentry))
                 goto done;
 
-        /* This is an autofs submount, we can't expire it */
-        if (is_autofs4_dentry(dentry))
-                goto done;
+        if (is_autofs4_dentry(dentry)) {
+                struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
+
+                /* This is an autofs submount, we can't expire it */
+                if (sbi->type == AUTOFS_TYPE_INDIRECT)
+                        goto done;
+
+                /*
+                 * Otherwise it's an offset mount and we need to check
+                 * if we can umount its mount, if there is one.
+                 */
+                if (!d_mountpoint(dentry))
+                        goto done;
+        }
 
         /* Update the expiry counter if fs is busy */
         if (!may_umount_tree(mnt)) {