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

From: Eric W. Biederman
Date: Mon Sep 24 2012 - 23:39:15 EST


Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx> writes:

> This reverts commit ee3efa91e240f513898050ef305a49a653c8ed90.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
>
> 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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