nfsd: Ensure sampling of the write verifier is atomic with the write

When doing an unstable write, we need to ensure that we sample the
write verifier before releasing the lock, and allowing a commit to
the same file to proceed.

Signed-off-by: Trond Myklebust <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

fs/nfsd/nfs3proc.c

···
 		RETURN_STATUS(nfserr_io);
 	nfserr = nfsd_write(rqstp, &resp->fh, argp->offset,
 			    rqstp->rq_vec, nvecs, &cnt,
-			    resp->committed);
+			    resp->committed, resp->verf);
 	resp->count = cnt;
 	RETURN_STATUS(nfserr);
 }

fs/nfsd/nfs3xdr.c

···
 nfs3svc_encode_writeres(struct svc_rqst *rqstp, __be32 *p)
 {
 	struct nfsd3_writeres *resp = rqstp->rq_resp;
-	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
-	__be32 verf[2];
 
 	p = encode_wcc_data(rqstp, p, &resp->fh);
 	if (resp->status == 0) {
 		*p++ = htonl(resp->count);
 		*p++ = htonl(resp->committed);
-		/* unique identifier, y2038 overflow can be ignored */
-		nfsd_copy_boot_verifier(verf, nn);
-		*p++ = verf[0];
-		*p++ = verf[1];
+		*p++ = resp->verf[0];
+		*p++ = resp->verf[1];
 	}
 	return xdr_ressize_check(rqstp, p);
 }

fs/nfsd/nfs4proc.c

···
 	}
 
 	write->wr_how_written = write->wr_stable_how;
-	gen_boot_verifier(&write->wr_verifier, SVC_NET(rqstp));
 
 	nvecs = svc_fill_write_vector(rqstp, write->wr_pagelist,
 				      &write->wr_head, write->wr_buflen);
···
 
 	status = nfsd_vfs_write(rqstp, &cstate->current_fh, nf,
 				write->wr_offset, rqstp->rq_vec, nvecs, &cnt,
-				write->wr_how_written);
+				write->wr_how_written,
+				(__be32 *)write->wr_verifier.data);
 	nfsd_file_put(nf);
 
 	write->wr_bytes_written = cnt;

fs/nfsd/nfsproc.c

···
 		return nfserr_io;
 	nfserr = nfsd_write(rqstp, fh_copy(&resp->fh, &argp->fh),
 			    argp->offset, rqstp->rq_vec, nvecs,
-			    &cnt, NFS_DATA_SYNC);
+			    &cnt, NFS_DATA_SYNC, NULL);
 	return nfsd_return_attrs(nfserr, resp);
 }
 

fs/nfsd/vfs.c

···
 __be32
 nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 				loff_t offset, struct kvec *vec, int vlen,
-				unsigned long *cnt, int stable)
+				unsigned long *cnt, int stable,
+				__be32 *verf)
 {
 	struct file		*file = nf->nf_file;
 	struct svc_export	*exp;
···
 		up_write(&nf->nf_rwsem);
 	} else {
 		down_read(&nf->nf_rwsem);
+		if (verf)
+			nfsd_copy_boot_verifier(verf,
+					net_generic(SVC_NET(rqstp),
+					nfsd_net_id));
 		host_err = vfs_iter_write(file, &iter, &pos, flags);
 		up_read(&nf->nf_rwsem);
 	}
···
  */
 __be32
 nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t offset,
-	   struct kvec *vec, int vlen, unsigned long *cnt, int stable)
+	   struct kvec *vec, int vlen, unsigned long *cnt, int stable,
+	   __be32 *verf)
 {
 	struct nfsd_file *nf;
 	__be32 err;
···
 		goto out;
 
 	err = nfsd_vfs_write(rqstp, fhp, nf, offset, vec,
-			vlen, cnt, stable);
+			vlen, cnt, stable, verf);
 	nfsd_file_put(nf);
 out:
 	trace_nfsd_write_done(rqstp, fhp, offset, *cnt);

fs/nfsd/vfs.h

···
 				loff_t, struct kvec *, int, unsigned long *,
 				u32 *eof);
 __be32 		nfsd_write(struct svc_rqst *, struct svc_fh *, loff_t,
-				struct kvec *, int, unsigned long *, int);
+				struct kvec *, int, unsigned long *,
+				int stable, __be32 *verf);
 __be32		nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 				struct nfsd_file *nf, loff_t offset,
 				struct kvec *vec, int vlen, unsigned long *cnt,
-				int stable);
+				int stable, __be32 *verf);
 __be32		nfsd_readlink(struct svc_rqst *, struct svc_fh *,
 				char *, int *);
 __be32		nfsd_symlink(struct svc_rqst *, struct svc_fh *,

fs/nfsd/xdr3.h

···
 	struct svc_fh		fh;
 	unsigned long		count;
 	int			committed;
+	__be32			verf[2];
 };
 
 struct nfsd3_renameres {