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

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Date:	Wed, 23 Jul 2014 14:06:43 +0800
From:	Ian Kent <raven@...maw.net>
To:	Vasily Averin <vvs@...allels.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Richard Weinberger <richard.weinberger@...il.com>
Subject: Re: [PATCH  v4] fs: umount on symlink leaks mnt count

On Mon, 2014-07-21 at 12:30 +0400, Vasily Averin wrote:
> 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>

Acked-by: Ian Kent <raven@...maw.net>

I was working on this too.
I prefer this patch over my own.
Haven't tested it yet but it is very similar to the patch I was working
with which had seen some basic testing.

> ---
>  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:


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