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

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2024-07-26 at 09:54 -0400, Jeff Layton wrote:
> On Wed, 2024-07-24 at 10:01 -0700, 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);
> 
> In the case where we have multiple stateids for this client, are we
> guaranteed to get back the delegation stateid here? What if we get
> back
> the open stateid for the O_WRONLY open instead?
> 

Oh, duh -- disregard this. We're looking for a specific stateid here,
so if the client sends a delegation stateid, that's what we'll find.
 
> 
> > +	/*
> > +	 * 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 */
> > +		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;
> > +	}

^^^
I do agree with Chuck that this looks sketchy.

> >  	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 {
> 

-- 
Jeff Layton <jlayton@kernel.org>