nfsd: move nfsd_debugfs_init() after nfsd4_init_slabs() in init_nfsd()

nfsd_debugfs_init() runs before nfsd4_init_slabs() in init_nfsd().
If the slab allocation fails, the bare "return retval" bypasses
nfsd_debugfs_exit(), leaving orphan debugfs files with stale fops
pointers into the freed module text.

Move nfsd_debugfs_init() to after the slab init succeeds, so the
early return has no debugfs state to clean up.

Since debugfs is now the more recently initialized of the two, also
update the unwind paths to match reverse-initialization (LIFO) order:
run nfsd_debugfs_exit() before nfsd4_free_slabs() in both the
init_nfsd() error path and exit_nfsd(). The nfsd debugfs files only
reference module-global state and have no dependency on the slab
caches, so that reordering is a cleanup with no functional change.

Fixes: 9fe5ea760e64 ("NFSD: Add /sys/kernel/debug/nfsd")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260611-nfsd-testing-v2-17-5b90e276f2d9@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index c9004f1dab0b..11bbc7e8210c 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2538,11 +2538,12 @@ static int __init init_nfsd(void)
 {
 	int retval;
 
-	nfsd_debugfs_init();
-
 	retval = nfsd4_init_slabs();
 	if (retval)
 		return retval;
+
+	nfsd_debugfs_init();
+
 	retval = nfsd4_init_pnfs();
 	if (retval)
 		goto out_free_slabs;
@@ -2587,8 +2588,8 @@ out_free_lockd:
 out_free_pnfs:
 	nfsd4_exit_pnfs();
 out_free_slabs:
-	nfsd4_free_slabs();
 	nfsd_debugfs_exit();
+	nfsd4_free_slabs();
 	return retval;
 }
 
@@ -2603,9 +2604,9 @@ static void __exit exit_nfsd(void)
 	unregister_pernet_subsys(&nfsd_net_ops);
 	nfsd_drc_slab_free();
 	nfsd_lockd_shutdown();
-	nfsd4_free_slabs();
 	nfsd4_exit_pnfs();
 	nfsd_debugfs_exit();
+	nfsd4_free_slabs();
 }
 
 MODULE_AUTHOR("Olaf Kirch <okir@monad.swb.de>");