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

When we have a successful commit, ensure we sample the commit verifier
before releasing the lock.

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

fs/nfsd/nfs3proc.c

···
 		RETURN_STATUS(nfserr_inval);
 
 	fh_copy(&resp->fh, &argp->fh);
-	nfserr = nfsd_commit(rqstp, &resp->fh, argp->offset, argp->count);
+	nfserr = nfsd_commit(rqstp, &resp->fh, argp->offset, argp->count,
+			resp->verf);
 
 	RETURN_STATUS(nfserr);
 }

fs/nfsd/nfs3xdr.c

···
 nfs3svc_encode_commitres(struct svc_rqst *rqstp, __be32 *p)
 {
 	struct nfsd3_commitres *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);
 	/* Write verifier */
 	if (resp->status == 0) {
-		/* 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

···
 {
 	struct nfsd4_commit *commit = &u->commit;
 
-	gen_boot_verifier(&commit->co_verf, SVC_NET(rqstp));
 	return nfsd_commit(rqstp, &cstate->current_fh, commit->co_offset,
-			     commit->co_count);
+			     commit->co_count,
+			     (__be32 *)commit->co_verf.data);
 }
 
 static __be32

fs/nfsd/vfs.c

···
  */
 __be32
 nfsd_commit(struct svc_rqst *rqstp, struct svc_fh *fhp,
-               loff_t offset, unsigned long count)
+               loff_t offset, unsigned long count, __be32 *verf)
 {
 	struct nfsd_file	*nf;
 	loff_t			end = LLONG_MAX;
···
 		err2 = vfs_fsync_range(nf->nf_file, offset, end, 0);
 		switch (err2) {
 		case 0:
+			nfsd_copy_boot_verifier(verf, net_generic(nf->nf_net,
+						nfsd_net_id));
 			break;
 		case -EINVAL:
 			err = nfserr_notsupp;
···
 						 nfsd_net_id));
 		}
 		up_write(&nf->nf_rwsem);
-	}
+	} else
+		nfsd_copy_boot_verifier(verf, net_generic(nf->nf_net,
+					nfsd_net_id));
 
 	nfsd_file_put(nf);
 out:

fs/nfsd/vfs.h

···
 				struct svc_fh *res, int createmode,
 				u32 *verifier, bool *truncp, bool *created);
 __be32		nfsd_commit(struct svc_rqst *, struct svc_fh *,
-				loff_t, unsigned long);
+				loff_t, unsigned long, __be32 *verf);
 #endif /* CONFIG_NFSD_V3 */
 int 		nfsd_open_break_lease(struct inode *, int);
 __be32		nfsd_open(struct svc_rqst *, struct svc_fh *, umode_t,

fs/nfsd/xdr3.h

···
 struct nfsd3_commitres {
 	__be32			status;
 	struct svc_fh		fh;
+	__be32			verf[2];
 };
 
 struct nfsd3_getaclres {