linux-kernel - Re: [PATCH] Revert "__d_unalias() should refuse to move mountpoints"

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Date:	Mon, 24 Sep 2012 20:39:17 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
Cc:	al viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "__d_unalias() should refuse to move mountpoints"

Maarten Lankhorst <maarten.lankhorst@...onical.com> writes:

> This reverts commit ee3efa91e240f513898050ef305a49a653c8ed90.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@...onical.com>
>
> My thread about the regression seemed to have been ignored, so I can only
> conclude nobody objects against a full revert of this patch.
>
> My testcase is simply booting through netboot with / and ~/nfs as separate
> nfs filesystems, then doing 'ls ~/nfs' followed by 'ls ~' in a gnome-terminal
> window, then I get:

Do I read your description correctly:  Without using a bind mount you
have the same nfs filesystem mounted on / and on ~/nfs?

Something is definitely off with your configuration but if to work you
need to move mount points around then that something seems much deeper
than the __d_unalias change.

What filesystems do you have mounted where?

> ls: cannot access nfs: Device or resource busy
>
> Similar things seem to happen with ls /, /dev /proc and /sys will no longer work.
>
> Reverting this patch seems to make things work again.
>
> ---
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 16521a9..711f421 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2387,13 +2387,14 @@ static struct dentry *__d_unalias(struct inode *inode,
>  		struct dentry *dentry, struct dentry *alias)
>  {
>  	struct mutex *m1 = NULL, *m2 = NULL;
> -	struct dentry *ret = ERR_PTR(-EBUSY);
> +	struct dentry *ret;
>  
>  	/* If alias and dentry share a parent, then no extra locks required */
>  	if (alias->d_parent == dentry->d_parent)
>  		goto out_unalias;
>  
>  	/* See lock_rename() */
> +	ret = ERR_PTR(-EBUSY);
>  	if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
>  		goto out_err;
>  	m1 = &dentry->d_sb->s_vfs_rename_mutex;
> @@ -2401,10 +2402,8 @@ static struct dentry *__d_unalias(struct inode *inode,
>  		goto out_err;
>  	m2 = &alias->d_parent->d_inode->i_mutex;
>  out_unalias:
> -	if (likely(!d_mountpoint(alias))) {
> -		__d_move(alias, dentry);
> -		ret = alias;
> -	}
> +	__d_move(alias, dentry);
> +	ret = alias;
>  out_err:
>  	spin_unlock(&inode->i_lock);
>  	if (m2)
>
> --
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