[PATCH 3/4] Do not allow umounting of frozen filesystems

["Fernando Luis Vázquez Cao" <fernando@oss.ntt.co.jp>]

Instead of making umount users wait until the filesystem is
unfreezed return EBUSY, which is very convenient in HA
configurations.

This could have been implemented at a lower level but it would
require considerable plumbing in functions such as release_mounts
which do not return errors.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
---

diff -urNp linux-2.6.31-rc7-orig/fs/namespace.c linux-2.6.31-rc7/fs/namespace.c
--- linux-2.6.31-rc7-orig/fs/namespace.c	2009-08-27 19:34:35.000000000 +0900
+++ linux-2.6.31-rc7/fs/namespace.c	2009-08-27 22:45:14.000000000 +0900
@@ -1086,6 +1086,14 @@ static int do_umount(struct vfsmount *mn
  		return retval;
  	}

+	if (sb->s_bdev != NULL) {
+		mutex_lock(&sb->s_bdev->bd_fsfreeze_mutex);
+		if (sb->s_frozen != SB_UNFROZEN) {
+			mutex_unlock(&sb->s_bdev->bd_fsfreeze_mutex);
+			return -EBUSY;
+		}
+	}
+
  	down_write(&namespace_sem);
  	spin_lock(&vfsmount_lock);
  	event++;
@@ -1104,6 +1112,10 @@ static int do_umount(struct vfsmount *mn
  		security_sb_umount_busy(mnt);
  	up_write(&namespace_sem);
  	release_mounts(&umount_list);
+
+	if (sb->s_bdev != NULL)
+		mutex_unlock(&sb->s_bdev->bd_fsfreeze_mutex);
+
  	return retval;
  }