[PATCH 5.4 36/65] nfsd4: fix nfsdfs reference count loop

[Greg Kroah-Hartman]

From: J. Bruce Fields <bfie...@redhat.com>

[ Upstream commit 681370f4b00af0fcc65bbfb9f82de526ab7ceb0a ]

We don't drop the reference on the nfsdfs filesystem with
mntput(nn->nfsd_mnt) until nfsd_exit_net(), but that won't be called
until the nfsd module's unloaded, and we can't unload the module as long
as there's a reference on nfsdfs.  So this prevents module unloading.

Fixes: 2c830dd7209b ("nfsd: persist nfsd filesystem across mounts")
Reported-and-Tested-by:  Luo Xiaogang <lxg...@163.com>
Signed-off-by: J. Bruce Fields <bfie...@redhat.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 fs/nfsd/nfs4state.c |  8 +++++++-
 fs/nfsd/nfsctl.c    | 22 ++++++++++++----------
 fs/nfsd/nfsd.h      |  3 +++
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 1e8f5e281bb53..fa3dcaa82572e 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -7719,9 +7719,14 @@ nfs4_state_start_net(struct net *net)
        struct nfsd_net *nn = net_generic(net, nfsd_net_id);
        int ret;
 
-       ret = nfs4_state_create_net(net);
+       ret = get_nfsdfs(net);
        if (ret)
                return ret;
+       ret = nfs4_state_create_net(net);
+       if (ret) {
+               mntput(nn->nfsd_mnt);
+               return ret;
+       }
        locks_start_grace(net, &nn->nfsd4_manager);
        nfsd4_client_tracking_init(net);
        if (nn->track_reclaim_completes && nn->reclaim_str_hashtbl_size == 0)
@@ -7790,6 +7795,7 @@ nfs4_state_shutdown_net(struct net *net)
 
        nfsd4_client_tracking_exit(net);
        nfs4_state_destroy_net(net);
+       mntput(nn->nfsd_mnt);
 }
 
 void
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 159feae6af8ba..596ed6a42022d 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1424,6 +1424,18 @@ static struct file_system_type nfsd_fs_type = {
 };
 MODULE_ALIAS_FS("nfsd");
 
+int get_nfsdfs(struct net *net)
+{
+       struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+       struct vfsmount *mnt;
+
+       mnt =  vfs_kern_mount(&nfsd_fs_type, SB_KERNMOUNT, "nfsd", NULL);
+       if (IS_ERR(mnt))
+               return PTR_ERR(mnt);
+       nn->nfsd_mnt = mnt;
+       return 0;
+}
+
 #ifdef CONFIG_PROC_FS
 static int create_proc_exports_entry(void)
 {
@@ -1452,7 +1464,6 @@ unsigned int nfsd_net_id;
 static __net_init int nfsd_init_net(struct net *net)
 {
        int retval;
-       struct vfsmount *mnt;
        struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
        retval = nfsd_export_init(net);
@@ -1479,16 +1490,8 @@ static __net_init int nfsd_init_net(struct net *net)
        init_waitqueue_head(&nn->ntf_wq);
        seqlock_init(&nn->boot_lock);
 
-       mnt =  vfs_kern_mount(&nfsd_fs_type, SB_KERNMOUNT, "nfsd", NULL);
-       if (IS_ERR(mnt)) {
-               retval = PTR_ERR(mnt);
-               goto out_mount_err;
-       }
-       nn->nfsd_mnt = mnt;
        return 0;
 
-out_mount_err:
-       nfsd_reply_cache_shutdown(nn);
 out_drc_error:
        nfsd_idmap_shutdown(net);
 out_idmap_error:
@@ -1501,7 +1504,6 @@ static __net_exit void nfsd_exit_net(struct net *net)
 {
        struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-       mntput(nn->nfsd_mnt);
        nfsd_reply_cache_shutdown(nn);
        nfsd_idmap_shutdown(net);
        nfsd_export_shutdown(net);
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 7a835fb7d79f7..65097324b42a0 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -89,6 +89,8 @@ void          nfsd_destroy(struct net *net);
 
 bool           i_am_nfsd(void);
 
+int get_nfsdfs(struct net *);
+
 struct nfsdfs_client {
        struct kref cl_ref;
        void (*cl_release)(struct kref *kref);
@@ -99,6 +101,7 @@ struct dentry *nfsd_client_mkdir(struct nfsd_net *nn,
                struct nfsdfs_client *ncl, u32 id, const struct tree_descr *);
 void nfsd_client_rmdir(struct dentry *dentry);
 
+
 #if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
 #ifdef CONFIG_NFSD_V2_ACL
 extern const struct svc_version nfsd_acl_version2;
-- 
2.25.1