linux-kernel - [PATCH v4] fs: umount on symlink leaks mnt count

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Message-ID: <53CCCF9F.6090301@parallels.com>
Date:	Mon, 21 Jul 2014 12:30:23 +0400
From:	Vasily Averin <vvs@...allels.com>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Richard Weinberger <richard.weinberger@...il.com>
Subject: [PATCH  v4] fs: umount on symlink leaks mnt count

v4: description corrected
v3: patch inline

Currently umount on symlink blocks following umount:

/vz is separate mount

# ls /vz/ -al | grep test
drwxr-xr-x.  2 root root       4096 Jul 19 01:14 testdir
lrwxrwxrwx.  1 root root         11 Jul 19 01:16 testlink -> /vz/testdir
# umount -l /vz/testlink
umount: /vz/testlink: not mounted (expected)

# lsof /vz
# umount /vz
umount: /vz: device is busy. (unexpected)

In this case mountpoint_last() gets an extra refcount on path->mnt

Signed-off-by: Vasily Averin <vvs@...nvz.org>
---
 fs/namei.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 985c6f3..9eb787e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2256,9 +2256,10 @@ done:
 		goto out;
 	}
 	path->dentry = dentry;
-	path->mnt = mntget(nd->path.mnt);
+	path->mnt = nd->path.mnt;
 	if (should_follow_link(dentry, nd->flags & LOOKUP_FOLLOW))
 		return 1;
+	mntget(path->mnt);
 	follow_mount(path);
 	error = 0;
 out:
-- 
1.7.5.4

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