Re: [PATCH] dmaengine: Free channel ID after device_unregister()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found no new issues
in this patch, but noticed 1 related pre-existing issue it does not
introduce:
- [Medium] dmaengine: IDA leak on error path in
  dma_async_device_register() [1]
--

commit e2b5dc17e7cb70401abfdf640998b8028522d873
Author: Zhejun Huang <zhejun_huang@linux.alibaba.com>

dmaengine: Free channel ID after device_unregister()

This commit moves the ida_free() call in
__dma_async_device_channel_unregister() after device_unregister() so that a
concurrent channel registration cannot reuse the channel ID before the old
device name is removed.

> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 34be53487a21d..2642abf105d76 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -1171,8 +1171,8 @@ static void __dma_async_device_channel_unregister(struct dma_device *device,
>  	device->chancnt--;
>  	chan->chan_dev->chan = NULL;
>  	mutex_unlock(&dma_list_mutex);
> -	ida_free(&device->chan_ida, chan->chan_id);
>  	device_unregister(dmaengine_chan_dev(chan));
> +	ida_free(&device->chan_ida, chan->chan_id);
>  	free_percpu(chan->local);
>  }

[Severity: Medium]
This problem wasn't introduced by this patch, but does the error path in
dma_async_device_register() leak IDs from device->chan_ida and dma_ida
[1]?

drivers/dma/dmaengine.c:dma_async_device_register() {
    ...
err_out:
	/* if we never registered a channel just release the idr */
	if (!device->chancnt) {
		ida_free(&dma_ida, device->dev_id);
		return rc;
	}

	list_for_each_entry(chan, &device->channels, device_node) {
		if (chan->local == NULL)
			continue;
		mutex_lock(&dma_list_mutex);
		chan->chan_dev->chan = NULL;
		mutex_unlock(&dma_list_mutex);
		device_unregister(dmaengine_chan_dev(chan));
		free_percpu(chan->local);
	}
	return rc;
}

If registration fails after at least one channel has been registered (for
example, on a subsequent channel or in dma_chan_get()), device->chancnt is
non-zero.  The open-coded cleanup loop unregisters the channels without
freeing each chan->chan_id or destroying device->chan_ida, and
device->dev_id is never freed from dma_ida.

[1] https://sashiko.dev/#/bug/linux-39bbcde3-023e-41e2-afef-7a2c13f45a17

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110101607.13784-1-zhejun_huang@linux.alibaba.com?part=1