Re: [PATCH 19/19] nfs: switch to _async for all directory ops.

[Al Viro]

On Thu, Feb 06, 2025 at 04:42:56PM +1100, NeilBrown wrote:
>  nfs_sillyrename(struct inode *dir, struct dentry *dentry)
>  {
>  	static unsigned int sillycounter;
> @@ -447,7 +451,8 @@ nfs_sillyrename(struct inode *dir, struct dentry *dentry)
>  	struct dentry *sdentry;
>  	struct inode *inode = d_inode(dentry);
>  	struct rpc_task *task;
> -	int            error = -EBUSY;
> +	struct dentry *base;
> +	int error = -EBUSY;
>  
>  	dfprintk(VFS, "NFS: silly-rename(%pd2, ct=%d)\n",
>  		dentry, d_count(dentry));
> @@ -461,10 +466,11 @@ nfs_sillyrename(struct inode *dir, struct dentry *dentry)
>  
>  	fileid = NFS_FILEID(d_inode(dentry));
>  
> +	base = d_find_alias(dir);

Huh?  That would better be dentry->d_parent and all operations are in
that directory, so you don't even need to grab a reference...

>  	sdentry = NULL;
>  	do {
>  		int slen;
> -		dput(sdentry);
> +
>  		sillycounter++;
>  		slen = scnprintf(silly, sizeof(silly),
>  				SILLYNAME_PREFIX "%0*llx%0*x",
> @@ -474,14 +480,19 @@ nfs_sillyrename(struct inode *dir, struct dentry *dentry)
>  		dfprintk(VFS, "NFS: trying to rename %pd to %s\n",
>  				dentry, silly);
>  
> -		sdentry = lookup_one_len(silly, dentry->d_parent, slen);
> -		/*
> -		 * N.B. Better to return EBUSY here ... it could be
> -		 * dangerous to delete the file while it's in use.
> -		 */
> -		if (IS_ERR(sdentry))
> -			goto out;
> -	} while (d_inode(sdentry) != NULL); /* need negative lookup */
> +		sdentry = lookup_and_lock_one(NULL, silly, slen,
> +					      base,
> +					      LOOKUP_CREATE | LOOKUP_EXCL
> +					      | LOOKUP_RENAME_TARGET
> +					      | LOOKUP_PARENT_LOCKED);
> +	} while (PTR_ERR_OR_ZERO(sdentry) == -EEXIST); /* need negative lookup */

What's wrong with sdentry == ERR_PTR(-EEXIST)?