Re: [PATCH v2 03/14] NTB: ntb_transport: Avoid deadlock when cancelling link work

[Frank Li <Frank.li@oss.nxp.com>]

On Thu, Sep 10, 2026 at 01:08:25PM +0900, Koichiro Den wrote:
> During initial link setup, ntb_transport_link_work() can retry with
> nt->link_is_up still false. A retry can block on link_event_lock
> while cleanup holds it and waits in cancel_delayed_work_sync(),
> leading to deadlock.
>
> Move the conditional cancellation outside link_event_lock, before
> QP cleanup. Keep QP cleanup and MW release under the lock so link
> work cannot restart QPs between them. Put the locking in
> ntb_transport_link_cleanup() to cover both worker and remove paths.
>
> Fixes: 3db835dd8f9a ("ntb: Add mutex to make link_event_callback executed linearly.")
> Cc: stable@vger.kernel.org
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> ---
> Changes in v2:
>   - No changes.
>
>  drivers/ntb/ntb_transport.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> index 55a20ae9a85e..c77b173dca01 100644
> --- a/drivers/ntb/ntb_transport.c
> +++ b/drivers/ntb/ntb_transport.c
> @@ -960,6 +960,15 @@ static void ntb_transport_link_cleanup(struct ntb_transport_ctx *nt)
>  	struct ntb_transport_qp *qp;
>  	u64 qp_bitmap_alloc;
>  	unsigned int i, count;
> +	bool cancel_link_work;
> +
> +	scoped_guard(mutex, &nt->link_event_lock)
> +		cancel_link_work = !nt->link_is_up;
> +
> +	if (cancel_link_work)
> +		cancel_delayed_work_sync(&nt->link_work);

what happen if schedule new work here?

Frank
> +
> +	guard(mutex)(&nt->link_event_lock);
>
>  	qp_bitmap_alloc = nt->qp_bitmap & ~nt->qp_bitmap_free;
>
> @@ -972,9 +981,6 @@ static void ntb_transport_link_cleanup(struct ntb_transport_ctx *nt)
>  			cancel_delayed_work_sync(&qp->link_work);
>  		}
>
> -	if (!nt->link_is_up)
> -		cancel_delayed_work_sync(&nt->link_work);
> -
>  	for (i = 0; i < nt->mw_count; i++)
>  		ntb_free_mw(nt, i);
>
> @@ -992,7 +998,6 @@ static void ntb_transport_link_cleanup_work(struct work_struct *work)
>  	struct ntb_transport_ctx *nt =
>  		container_of(work, struct ntb_transport_ctx, link_cleanup);
>
> -	guard(mutex)(&nt->link_event_lock);
>  	ntb_transport_link_cleanup(nt);
>  }
>
> --
> 2.51.0
>