[PATCH] nfsd: fix handling of readdir in v4root vs. mount upcall timeout

[Jeff Layton <jlayton@kernel.org>]

If v4 READDIR operation hits a mountpoint and gets back an error,
then it will include that entry in the reply and set RDATTR_ERROR for it
to the error.

That's fine for "normal" exported filesystems, but on the v4root, we
need to be more careful to only expose the existence of dentries that
lead to exports.

If the mountd upcall times out while checking to see whether a
mountpoint on the v4root is exported, then we have no recourse other
than to fail the whole operation.

Cc: Steve Dickson <steved@redhat.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216777
Reported-by:  JianHong Yin <yin-jianhong@163.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfs4xdr.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 2b4ae858c89b..984528ce8d68 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3588,6 +3588,7 @@ nfsd4_encode_dirent(void *ccdv, const char *name, int namlen,
 	struct readdir_cd *ccd = ccdv;
 	struct nfsd4_readdir *cd = container_of(ccd, struct nfsd4_readdir, common);
 	struct xdr_stream *xdr = cd->xdr;
+	struct svc_export *exp = cd->rd_fhp->fh_export;
 	int start_offset = xdr->buf->len;
 	int cookie_offset;
 	u32 name_and_cookie;
@@ -3629,6 +3630,17 @@ nfsd4_encode_dirent(void *ccdv, const char *name, int namlen,
 	case nfserr_noent:
 		xdr_truncate_encode(xdr, start_offset);
 		goto skip_entry;
+	case nfserr_jukebox:
+		/*
+		 * The pseudoroot should only display dentries that lead to
+		 * exports. If we get EJUKEBOX here, then we can't tell whether
+		 * this entry should be included. Just fail the whole READDIR
+		 * with NFS4ERR_DELAY in that case, and hope that the situation
+		 * will resolve itself by the client's next attempt.
+		 */
+		if (exp->ex_flags & NFSEXP_V4ROOT)
+			goto fail;
+		fallthrough;
 	default:
 		/*
 		 * If the client requested the RDATTR_ERROR attribute,
-- 
2.38.1