On Wed, Nov 19, 2025 at 07:37:10PM -0800, Bobby Eshleman wrote:
...
> @@ -292,25 +327,67 @@ net_devmem_bind_dmabuf(struct net_device *dev,
...
> + /* Enforce system-wide autorelease mode consistency for RX bindings.
> + * TX bindings don't use autorelease (always false) since tokens aren't
> + * leaked in TX path. Only RX bindings must all have the same
> + * autorelease mode, never mixed.
> + *
> + * We use the xarray's lock to atomically check xa_empty() and toggle
> + * the static key, avoiding the race where two new bindings may try to
> + * set the static key to different states.
> + */
> + xa_lock(&net_devmem_dmabuf_bindings);
> +
> + if (direction == DMA_FROM_DEVICE) {
> + if (!xa_empty(&net_devmem_dmabuf_bindings)) {
> + bool mode;
> +
> + mode = static_key_enabled(&tcp_devmem_ar_key);
> +
> + /* When bindings exist, enforce that the mode does not
> + * change.
> + */
> + if (mode != autorelease) {
> + NL_SET_ERR_MSG_FMT(extack,
> + "System already configured
> with autorelease=%d",
> + mode);
> + err = -EINVAL;
> + goto err_unlock_xa;
> + }
> + } else {
> + /* First binding sets the mode for all subsequent
> + * bindings.
> + */
> + if (autorelease)
> + static_branch_enable(&tcp_devmem_ar_key);
> + else
> + static_branch_disable(&tcp_devmem_ar_key);
Hi Bobby,
This code runs inside xa_lock, which is a spinlock.
But static_branch_enable() and static_branch_disable()
may sleep due to some combination of taking a mutex
and cpu_read_lock.
Flagged by Claude Code with https://github.com/masoncl/review-prompts/
> + }
> + }
> +
> + err = __xa_alloc_cyclic(&net_devmem_dmabuf_bindings, &binding->id,
> + binding, xa_limit_32b, &id_alloc_next,
> + GFP_KERNEL);
> if (err < 0)
> - goto err_free_chunks;
> + goto err_unlock_xa;
> +
> + xa_unlock(&net_devmem_dmabuf_bindings);
>
> list_add(&binding->list, &priv->bindings);
>
> return binding;
>
> +err_unlock_xa:
> + xa_unlock(&net_devmem_dmabuf_bindings);
...
