When the NFSD instance doesn't to startup, the net ref data memory is
not properly reclaimed, which triggers the memory leak issue reported
by syzbot [1].

To avoid the problem reported in [1], the net ref data memory reclamation
action is moved outside of nfsd_net_up when the net is shutdown.

[1]
BUG: memory leak
unreferenced object 0xffff88812a39dfc0 (size 64):
  backtrace (crc a2262fc6):
    percpu_ref_init+0x94/0x1e0 lib/percpu-refcount.c:76
    nfsd_create_serv+0xbe/0x260 fs/nfsd/nfssvc.c:605
    nfsd_nl_listener_set_doit+0x62/0xb00 fs/nfsd/nfsctl.c:1882
    genl_family_rcv_msg_doit+0x11e/0x190 net/netlink/genetlink.c:1115
    genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
    genl_rcv_msg+0x2fd/0x440 net/netlink/genetlink.c:1210
    
Reported-by: syzbot+6ee3b889bdeada0a6226@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6ee3b889bdeada0a6226
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/nfsd/nfssvc.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index b08ae85d53ef..e2b2cf0dd013 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -406,26 +406,26 @@ static void nfsd_shutdown_net(struct net *net)
 {
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	if (!nn->nfsd_net_up)
-		return;
-
-	percpu_ref_kill_and_confirm(&nn->nfsd_net_ref, nfsd_net_done);
-	wait_for_completion(&nn->nfsd_net_confirm_done);
-
-	nfsd_export_flush(net);
-	nfs4_state_shutdown_net(net);
-	nfsd_reply_cache_shutdown(nn);
-	nfsd_file_cache_shutdown_net(net);
-	if (nn->lockd_up) {
-		lockd_down(net);
-		nn->lockd_up = false;
+	if (nn->nfsd_net_up) {
+		percpu_ref_kill_and_confirm(&nn->nfsd_net_ref, nfsd_net_done);
+		wait_for_completion(&nn->nfsd_net_confirm_done);
+
+		nfsd_export_flush(net);
+		nfs4_state_shutdown_net(net);
+		nfsd_reply_cache_shutdown(nn);
+		nfsd_file_cache_shutdown_net(net);
+		if (nn->lockd_up) {
+			lockd_down(net);
+			nn->lockd_up = false;
+		}
+		wait_for_completion(&nn->nfsd_net_free_done);
 	}
 
-	wait_for_completion(&nn->nfsd_net_free_done);
 	percpu_ref_exit(&nn->nfsd_net_ref);
 
+	if (nn->nfsd_net_up)
+		nfsd_shutdown_generic();
 	nn->nfsd_net_up = false;
-	nfsd_shutdown_generic();
 }
 
 static DEFINE_SPINLOCK(nfsd_notifier_lock);
-- 
2.43.0

From: Chuck Lever <chuck.lever@oracle.com>

On Tue, 16 Dec 2025 18:27:37 +0800, Edward Adam Davis wrote:
> When the NFSD instance doesn't to startup, the net ref data memory is
> not properly reclaimed, which triggers the memory leak issue reported
> by syzbot [1].
> 
> To avoid the problem reported in [1], the net ref data memory reclamation
> action is moved outside of nfsd_net_up when the net is shutdown.
> 
> [...]

Applied to nfsd-testing, thanks!

[1/1] NFSD: net ref data still needs to be freed even if net hasn't startup
      commit: 339bafeb9942cb3f42c34ed5fcf1fbe377a492da

--
Chuck Lever