Re: [PATCH rfc 2/2] NFSD: allow client to use write delegation stateid for READ

[Dai Ngo <dai.ngo@oracle.com>]

On 7/24/24 10:01 AM, Sagi Grimberg wrote:
> Based on a patch fom Dai Ngo, allow NFSv4 client to use write delegation
> stateid for READ operation. Per RFC 8881 section 9.1.2. Use of the
> Stateid and Locking.
>
> In addition, for anonymous stateids, check for pending delegations by
> the filehandle and client_id, and if a conflict found, recall the delegation
> before allowing the read to take place.
>
> Suggested-by: Dai Ngo <dai.ngo@oracle.com>
> Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
> ---
>   fs/nfsd/nfs4proc.c  | 22 +++++++++++++++++++--
>   fs/nfsd/nfs4state.c | 47 +++++++++++++++++++++++++++++++++++++++++++++
>   fs/nfsd/nfs4xdr.c   |  9 +++++++++
>   fs/nfsd/state.h     |  2 ++
>   fs/nfsd/xdr4.h      |  2 ++
>   5 files changed, 80 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 7b70309ad8fb..324984ec70c6 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -979,8 +979,24 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>   	/* check stateid */
>   	status = nfs4_preprocess_stateid_op(rqstp, cstate, &cstate->current_fh,
>   					&read->rd_stateid, RD_STATE,
> -					&read->rd_nf, NULL);
> -
> +					&read->rd_nf, &read->rd_wd_stid);
> +	/*
> +	 * rd_wd_stid is needed for nfsd4_encode_read to allow write
> +	 * delegation stateid used for read. Its refcount is decremented
> +	 * by nfsd4_read_release when read is done.
> +	 */
> +	if (!status) {
> +		if (!read->rd_wd_stid) {
> +			/* special stateid? */
> +			status = nfsd4_deleg_read_conflict(rqstp, cstate->clp,
> +				&cstate->current_fh);
> +		} else if (read->rd_wd_stid->sc_type != SC_TYPE_DELEG ||
> +			   delegstateid(read->rd_wd_stid)->dl_type !=
> +						NFS4_OPEN_DELEGATE_WRITE) {
> +			nfs4_put_stid(read->rd_wd_stid);
> +			read->rd_wd_stid = NULL;
> +		}
> +	}
>   	read->rd_rqstp = rqstp;
>   	read->rd_fhp = &cstate->current_fh;
>   	return status;
> @@ -990,6 +1006,8 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>   static void
>   nfsd4_read_release(union nfsd4_op_u *u)
>   {
> +	if (u->read.rd_wd_stid)
> +		nfs4_put_stid(u->read.rd_wd_stid);
>   	if (u->read.rd_nf)
>   		nfsd_file_put(u->read.rd_nf);
>   	trace_nfsd_read_done(u->read.rd_rqstp, u->read.rd_fhp,
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index dc61a8adfcd4..7e6b9fb31a4c 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -8805,6 +8805,53 @@ nfsd4_get_writestateid(struct nfsd4_compound_state *cstate,
>   	get_stateid(cstate, &u->write.wr_stateid);
>   }
>   
> +/**
> + * nfsd4_deleg_read_conflict - Recall if read causes conflict
> + * @rqstp: RPC transaction context
> + * @clp: nfs client
> + * @fhp: nfs file handle
> + * @inode: file to be checked for a conflict
> + * @modified: return true if file was modified
> + * @size: new size of file if modified is true
> + *
> + * This function is called when there is a conflict between a write
> + * delegation and a read that is using a special stateid where the
> + * we cannot derive the client stateid exsistence. The server
> + * must recall a conflicting delegation before allowing the read
> + * to continue.
> + *
> + * Returns 0 if there is no conflict; otherwise an nfs_stat
> + * code is returned.
> + */
> +__be32 nfsd4_deleg_read_conflict(struct svc_rqst *rqstp,
> +		struct nfs4_client *clp, struct svc_fh *fhp)
> +{
> +	struct nfs4_file *fp;
> +	__be32 status = 0;
> +
> +	fp = nfsd4_file_hash_lookup(fhp);
> +	if (!fp)
> +		return nfs_ok;
> +
> +	spin_lock(&state_lock);
> +	spin_lock(&fp->fi_lock);
> +	if (!list_empty(&fp->fi_delegations) &&
> +	    !nfs4_delegation_exists(clp, fp)) {
> +		/* conflict, recall deleg */

I don't see how we can have a delegation conflict here. If a client
has a write delegation then there should not be any delegations from
other clients.

-Dai

> +		status = nfserrno(nfsd_open_break_lease(fp->fi_inode,
> +					NFSD_MAY_READ));
> +		if (status)
> +			goto out;
> +		if (!nfsd_wait_for_delegreturn(rqstp, fp->fi_inode))
> +			status = nfserr_jukebox;
> +	}
> +out:
> +	spin_unlock(&fp->fi_lock);
> +	spin_unlock(&state_lock);
> +	return status;
> +}
> +
> +
>   /**
>    * nfsd4_deleg_getattr_conflict - Recall if GETATTR causes conflict
>    * @rqstp: RPC transaction context
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index c7bfd2180e3f..f0fe526fac3c 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -4418,6 +4418,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
>   	unsigned long maxcount;
>   	struct file *file;
>   	__be32 *p;
> +	fmode_t o_fmode = 0;
>   
>   	if (nfserr)
>   		return nfserr;
> @@ -4437,10 +4438,18 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
>   	maxcount = min_t(unsigned long, read->rd_length,
>   			 (xdr->buf->buflen - xdr->buf->len));
>   
> +	if (read->rd_wd_stid) {
> +		/* allow READ using write delegation stateid */
> +		o_fmode = file->f_mode;
> +		file->f_mode |= FMODE_READ;
> +	}
>   	if (file->f_op->splice_read && splice_ok)
>   		nfserr = nfsd4_encode_splice_read(resp, read, file, maxcount);
>   	else
>   		nfserr = nfsd4_encode_readv(resp, read, file, maxcount);
> +	if (o_fmode)
> +		file->f_mode = o_fmode;
> +
>   	if (nfserr) {
>   		xdr_truncate_encode(xdr, starting_len);
>   		return nfserr;
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index ffc217099d19..c1f13b5877c6 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -780,6 +780,8 @@ static inline bool try_to_expire_client(struct nfs4_client *clp)
>   	return clp->cl_state == NFSD4_EXPIRABLE;
>   }
>   
> +extern __be32 nfsd4_deleg_read_conflict(struct svc_rqst *rqstp,
> +		struct nfs4_client *clp, struct svc_fh *fhp);
>   extern __be32 nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp,
>   		struct inode *inode, bool *file_modified, u64 *size);
>   #endif   /* NFSD4_STATE_H */
> diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
> index fbdd42cde1fa..434973a6a8b1 100644
> --- a/fs/nfsd/xdr4.h
> +++ b/fs/nfsd/xdr4.h
> @@ -426,6 +426,8 @@ struct nfsd4_read {
>   	struct svc_rqst		*rd_rqstp;          /* response */
>   	struct svc_fh		*rd_fhp;            /* response */
>   	u32			rd_eof;             /* response */
> +
> +	struct nfs4_stid	*rd_wd_stid;		/* internal */
>   };
>   
>   struct nfsd4_readdir {