Re: [PATCH] ocfs2/dlm: drain join handlers before releasing module text

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 10/20/26 9:04 PM, Cen Zhang wrote:
> 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
>   <preempted>
>                                        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 also
> covers partial registration and dlm_init() error unwind before module
> memory is released.
> 
> 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
>     Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc <cc> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> 
> Register dump omitted.
> 
>     Call Trace:
>      <TASK>
>      ? 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
>      </TASK>
>     Modules linked in: ocfs2_nodemanager [last unloaded: ocfs2_dlm]
>     ---[ end trace 0000000000000000 ]---
> 
> Fixes: 6714d8e86bf4 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
> Assisted-by: LLM
> ---
>  fs/ocfs2/dlm/dlmdomain.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c
> index 97bb9400e24b..0f4d29cbce81 100644
> --- a/fs/ocfs2/dlm/dlmdomain.c
> +++ b/fs/ocfs2/dlm/dlmdomain.c
> @@ -2215,7 +2215,7 @@ static LIST_HEAD(dlm_join_handlers);
>  
>  static void dlm_unregister_net_handlers(void)
>  {
> -	o2net_unregister_handler_list(&dlm_join_handlers);
> +	o2net_unregister_and_flush_handler_list(&dlm_join_handlers);
>  }
>  
>  static int dlm_register_net_handlers(void)

dlm_unregister_net_handlers() is also reached from the dlm_init() error
label on failures that happen before any handler was ever registered.
So in case of an empty dlm_join_handlers, o2net_unregister_handler_list()
walks nothing, but o2net_flush_wq() still takes o2net_wq_mutex and drains
the entire o2net workqueue.

Thanks,
Joseph