Re: [PATCH] NFS: Don't skip lookup when holding a delegation

[bfields@fieldses.org (J. Bruce Fields)]

On Wed, Jun 12, 2019 at 10:45:13AM -0400, Benjamin Coddington wrote:
> If we skip lookup revalidation while holding a delegation, we might miss
> that the file has changed directories on the server.

The delegation should prevent the file disappearing from this directory,
so if I've been following the discussion, the bug was due to overlooking
the case where the change happened before we got the delegation.  Given
that history it seems worth calling out that case specifically?

Maybe a comment along the lines of:

		/*
		 * Note that the file can't move while we hold a
		 * delegation.  But this dentry could have been cached
		 * before we got a delegation.  So it's only safe to
		 * skip revalidation when the parent directory is
		 * unchanged:
		 */

But maybe there's a pithier way to say that.

--b.

> The directory's
> change attribute should still be checked against the dentry's d_time to
> perform a complete revalidation.
> 
> Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> ---
>  fs/nfs/dir.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index a71d0b42d160..10cc684dc082 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -1269,12 +1269,13 @@ nfs_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
>  		goto out_bad;
>  	}
>  
> -	if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> -		return nfs_lookup_revalidate_delegated(dir, dentry, inode);
> -
>  	/* Force a full look up iff the parent directory has changed */
>  	if (!(flags & (LOOKUP_EXCL | LOOKUP_REVAL)) &&
>  	    nfs_check_verifier(dir, dentry, flags & LOOKUP_RCU)) {
> +
> +		if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> +			return nfs_lookup_revalidate_delegated(dir, dentry, inode);
> +
>  		error = nfs_lookup_verify_inode(inode, flags);
>  		if (error) {
>  			if (error == -ESTALE)
> @@ -1707,9 +1708,6 @@ nfs4_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
>  	if (inode == NULL)
>  		goto full_reval;
>  
> -	if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
> -		return nfs_lookup_revalidate_delegated(dir, dentry, inode);
> -
>  	/* NFS only supports OPEN on regular files */
>  	if (!S_ISREG(inode->i_mode))
>  		goto full_reval;
> -- 
> 2.20.1