linux-kernel - Re: [PATCH v3 105/110] namei: make unlazy_walk and terminate_walk handle nd->stack, add unlazy

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Date:	Fri, 15 May 2015 06:07:20 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Neil Brown <neilb@...e.de>, Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 105/110] namei: make unlazy_walk and terminate_walk
 handle nd->stack, add unlazy_link

On Tue, May 12, 2015 at 05:10:01AM +0100, Al Viro wrote:

> +static int unlazy_link(struct nameidata *nd, struct path *link, unsigned seq)
> +{
> +	if (unlikely(!legitimize_path(nd, link, seq))) {
> +		drop_links(nd);
> +		rcu_read_unlock();
> +		nd->flags &= ~LOOKUP_RCU;
> +		nd->path.mnt = NULL;
> +		nd->path.dentry = NULL;
> +		if (!(nd->flags & LOOKUP_ROOT))
> +			nd->root.mnt = NULL;

... and nd->depth should be set to 0, to avoid bogus path_put() on the
stuff in nd->stack[...].link when we get to terminate_walk().  Fixed and
folded.

> +	} else if (likely(unlazy_walk(nd, NULL, 0)) == 0) {
> +		return 0;
> +	}
> +	path_put(link);
> +	return -ECHILD;
> +}
> +
>  static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
>  {
>  	return dentry->d_op->d_revalidate(dentry, flags);
> @@ -1537,20 +1613,6 @@ static inline int handle_dots(struct nameidata *nd, int type)
>  	return 0;
>  }
>  
> -static void terminate_walk(struct nameidata *nd)
> -{
> -	if (!(nd->flags & LOOKUP_RCU)) {
> -		path_put(&nd->path);
> -	} else {
> -		nd->flags &= ~LOOKUP_RCU;
> -		if (!(nd->flags & LOOKUP_ROOT))
> -			nd->root.mnt = NULL;
> -		rcu_read_unlock();
> -	}
> -	while (unlikely(nd->depth))
> -		put_link(nd);
> -}
> -
>  static int pick_link(struct nameidata *nd, struct path *link,
>  		     struct inode *inode, unsigned seq)
>  {
> @@ -1561,13 +1623,12 @@ static int pick_link(struct nameidata *nd, struct path *link,
>  		return -ELOOP;
>  	}
>  	if (nd->flags & LOOKUP_RCU) {
> -		if (unlikely(nd->path.mnt != link->mnt ||
> -			     unlazy_walk(nd, link->dentry, seq))) {
> +		if (unlikely(unlazy_link(nd, link, seq)))
>  			return -ECHILD;
> -		}
> +	} else {
> +		if (link->mnt == nd->path.mnt)
> +			mntget(link->mnt);
>  	}
> -	if (link->mnt == nd->path.mnt)
> -		mntget(link->mnt);
>  	error = nd_alloc_stack(nd);
>  	if (unlikely(error)) {
>  		path_put(link);
> --
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