Re: [PATCH v2] NFS: Don't skip lookup when holding a delegation

From: "Benjamin Coddington" <bcodding@redhat.com>
To: trond.myklebust@hammerspace.com, anna.schumaker@netapp.com
Cc: linux-nfs@vger.kernel.org
Subject: Re: [PATCH v2] NFS: Don't skip lookup when holding a delegation
Date: Thu, 16 Jan 2020 10:19:06 -0500	[thread overview]
Message-ID: <6399DBA2-DA9D-40C3-80BC-6DCE94BB9C49@redhat.com> (raw)
In-Reply-To: <77be993185fa7f114f6856f74f2f7affb5bd411d.1568904510.git.bcodding@redhat.com>

I'd like to bump this one again while we're talking about 
lookup/revalidation.

We have folks that hit this problem in the field:
     - client caches a dentry
     - file gets moved
     - server gives out a delegation
     - client never notices the change because we always skip 
revalidation

Is this the wrong place to fix this?  Any other feedback?

Ben

On 19 Sep 2019, at 10:49, 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 directory's
> change attribute should still be checked against the dentry's d_time 
> to
> perform a complete revalidation.
>
> V2 - Add some commentary as suggested-by J. Bruce Fields.
>
> Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> ---
>  fs/nfs/dir.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index 0adfd8840110..8723e82f5c9d 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -1197,12 +1197,20 @@ 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)) {
> +
> +		/*
> +		 * 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:
> +		 */
> +		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)
> @@ -1635,9 +1643,6 @@ 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