nfsd: reduce want-write range in nfsd4_create_file()

nfsd4_create_file() needs write access to the mount for two purposes:

1/ to create/open the file.
2/ to set attributes on the newly created (or pre-existing) file.

Currently this is all handled by holding the write access across the
open and the setattr.  A subsequent patch will necessarily change how
write access is gained for the open.  So we reduce the range for the
first want_write, and add another one to cover setattr.  If we failed to
get write access, it is only fatal if there were attrs to set.

We call nfsd_create_setattr() if at all possible, even when no attrs, as
it also calls commit_metadata and we need to be certain that the file
creation has been synced.  If the mount became read-only since the
creation happened, we can safely assume that the sync happened as part
of that.

Signed-off-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260717093001.1972119-16-neilb@ownmail.net
Signed-off-by: Chuck Lever <cel@kernel.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 6dff6013a068..5e047469ba78 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -343,6 +343,8 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 			       &QSTR_LEN(open->op_fname, open->op_fnamelen));
 	if (IS_ERR(child)) {
 		status = nfserrno(PTR_ERR(child));
+		if (!want_write_err)
+			fh_drop_write(fhp);
 		goto out;
 	}
 	path.dentry = child;
@@ -377,6 +379,8 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		}
 	}
 	end_creating(child);
+	if (!want_write_err)
+		fh_drop_write(fhp);
 	if (status != nfs_ok)
 		goto out;
 
@@ -420,7 +424,16 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if ((iap->ia_valid & ATTR_SIZE) && (iap->ia_size == 0))
 		iap->ia_valid &= ~ATTR_SIZE;
 
-	status = nfsd_create_setattr(rqstp, fhp, resfhp, &attrs);
+	/* We will need write access to set the attrs */
+	want_write_err = fh_want_write(fhp);
+	if (!want_write_err) {
+		status = nfsd_create_setattr(rqstp, fhp,
+					     resfhp, &attrs);
+		fh_drop_write(fhp);
+	} else if (nfsd_attrs_valid(&attrs)) {
+		/* Needed write access */
+		status = nfserrno(want_write_err);
+	}
 
 	if (attrs.na_labelerr)
 		open->op_bmval[2] &= ~FATTR4_WORD2_SECURITY_LABEL;
@@ -431,8 +444,6 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (attrs.na_paclerr)
 		open->op_bmval[2] &= ~FATTR4_WORD2_POSIX_ACCESS_ACL;
 out:
-	if (!want_write_err)
-		fh_drop_write(fhp);
 	nfsd_attrs_free(&attrs);
 	return status;
 }