nfsd: fix dentry refcounting on create

b44061d0b9 introduced a dentry ref counting bug.  Previously we were
grabbing one ref to dchild in nfsd_create(), but with the creation of
nfsd_create_locked() we have a ref for dchild from the lookup in
nfsd_create(), and then another ref in nfsd_create_locked().  The ref
from the lookup in nfsd_create() is never dropped and results in
dentries still in use at unmount.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Fixes: b44061d0b9 "nfsd: reorganize nfsd_create"
Reported-by: kernel test robot <xiaolong.ye@intel.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index ba944123167b..ff476e654b8f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1252,10 +1252,13 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
         if (IS_ERR(dchild))
                 return nfserrno(host_err);
         err = fh_compose(resfhp, fhp->fh_export, dchild, fhp);
-        if (err) {
-                dput(dchild);
+        /*
+         * We unconditionally drop our ref to dchild as fh_compose will have
+         * already grabbed its own ref for it.
+         */
+        dput(dchild);
+        if (err)
                 return err;
-        }
         return nfsd_create_locked(rqstp, fhp, fname, flen, iap, type,
                                         rdev, resfhp);
 }