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

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Message-ID: <4A9692CF.80508@oss.ntt.co.jp>
Date:	Thu, 27 Aug 2009 23:06:07 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	Christoph Hellwig <hch@....de>
CC:	t-sato@...jp.nec.com, m-hamaguchi@...jp.nec.com,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Sandeen <sandeen@...hat.com>
Subject: [PATCH 3/4] Do not allow umounting of frozen filesystems

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@....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;
  }

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