The code for a registered DLM handler must remain resident until its last invocation finishes. dlm_unregister_net_handlers() only removes dlm_join_handlers from the o2net registry. o2net_handler_get() takes a kref on the wrapper, but that reference does not pin ocfs2_dlm text. o2net_process_message() calls nh_func after dropping o2net_handler_lock. With CONFIG_OCFS2_FS_O2CB=m, ocfs2_dlm can be loaded independently of ocfs2_stack_o2cb while nodemanager continues handling messages from a configured, heartbeating peer. If no dependent module or module reference prevents normal unload, the following ordering is possible: Receive worker Module unload -------------- ------------- o2net_handler_get() take wrapper kref drop handler lock dlm_exit() unregister handlers release DLM module text call saved nh_func in released module text Use o2net_unregister_and_flush_handler_list() in the shared DLM unregister helper. It first prevents new lookups, then waits for the ordered o2net workqueue to drain, including a concurrent destruction of that queue. The acquired invocation therefore finishes before dlm_exit() returns and the loader releases the callback code. The same helper covers partial registration and dlm_init() error unwind before module memory is released. Skip the drain when the private join-handler list is empty. Early dlm_init() failures can reach this helper before any handler has been published. Partial-registration failure also reaches it a second time after the first call has already unregistered and drained the list. Neither case needs to take o2net_wq_mutex or drain unrelated work. The list is changed only by serialized module init/exit paths; a nonempty list still uses the full unregister-and-flush helper. Oops report as below: Oops: int3: 0000 [#1] SMP KASAN NOPTI CPU: 2 UID: 0 PID: 54 Comm: kworker/u16:3 Not tainted 7.3.0-rc4-next-20260921-pmb-ocfs2-functional-v1+ #1 PREEMPT(lazy) Hardware identification omitted. Workqueue: o2net o2net_rx_until_empty [ocfs2_nodemanager] RIP: 0010:0xffffffffc0423871 [Instruction byte dump omitted.] Register dump omitted. Call Trace: ? o2net_rx_until_empty+0x19b1/0x3300 [ocfs2_nodemanager] ? __pfx_o2net_rx_until_empty+0x10/0x10 [ocfs2_nodemanager] ? lock_acquire+0x190/0x300 ? process_one_work+0x935/0x1b40 ? process_one_work+0x834/0x1b40 ? srso_alias_return_thunk+0x5/0xfbef5 ? lock_release+0xc8/0x290 ? srso_alias_return_thunk+0x5/0xfbef5 ? process_one_work+0x9a8/0x1b40 ? __pfx_process_one_work+0x10/0x10 ? lock_acquire+0x190/0x300 ? lock_is_held_type+0x8f/0x100 ? srso_alias_return_thunk+0x5/0xfbef5 ? worker_thread+0x65c/0xe40 ? srso_alias_return_thunk+0x5/0xfbef5 ? __kthread_parkme+0x177/0x220 ? srso_alias_return_thunk+0x5/0xfbef5 ? __pfx_worker_thread+0x10/0x10 ? kthread+0x351/0x460 ? srso_alias_return_thunk+0x5/0xfbef5 ? __pfx_kthread+0x10/0x10 ? ret_from_fork+0x659/0x940 ? __pfx_ret_from_fork+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? __switch_to+0x74f/0xf70 ? __pfx_kthread+0x10/0x10 ? ret_from_fork_asm+0x1a/0x30 Modules linked in: ocfs2_nodemanager [last unloaded: ocfs2_dlm] ---[ end trace 0000000000000000 ]--- Fixes: 6714d8e86bf4 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem") Cc: Signed-off-by: Cen Zhang Assisted-by: LLM --- Changes in v2: - Skip unregister-and-flush when the private join-handler list is empty, covering early dlm_init failures and the second cleanup after partial-registration unwind. - Retain the full unregister-and-flush helper for every nonempty list; do not change the generic o2net helper. Link to v1: https://lore.kernel.org/r/pm-ocfs2-objects-candidate-0076-v5-dd198d8a9358ad81f70e@gmail.com fs/ocfs2/dlm/dlmdomain.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c index 97bb9400e24b..a7dc3da6dfc7 100644 --- a/fs/ocfs2/dlm/dlmdomain.c +++ b/fs/ocfs2/dlm/dlmdomain.c @@ -2215,7 +2215,8 @@ static LIST_HEAD(dlm_join_handlers); static void dlm_unregister_net_handlers(void) { - o2net_unregister_handler_list(&dlm_join_handlers); + if (!list_empty(&dlm_join_handlers)) + o2net_unregister_and_flush_handler_list(&dlm_join_handlers); } static int dlm_register_net_handlers(void)