Re: crypto: ccp - Release dma channels before dmaengine unrgister

[Tom Lendacky <thomas.lendacky@amd.com>]

On 8/30/22 04:34, Koba Ko wrote:
> A warning is shown during shutdown,
> 
> __dma_async_device_channel_unregister called while 2 clients hold a reference
> WARNING: CPU: 15 PID: 1 at drivers/dma/dmaengine.c:1110
> __dma_async_device_channel_unregister
> 
> Call dma_release_channel for occupied channles
> before dma_async_device_unregister.
> 
> Fixes: 4cbe9bc34ed0 ("crypto: ccp - ccp_dmaengine_unregister release dma channels")
> Signed-off-by: Koba Ko <koba.ko@canonical.com>
> ---
>   drivers/crypto/ccp/ccp-dmaengine.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/crypto/ccp/ccp-dmaengine.c b/drivers/crypto/ccp/ccp-dmaengine.c
> index 7d4b4ad1db1f3..ba3eb1ac3b55d 100644
> --- a/drivers/crypto/ccp/ccp-dmaengine.c
> +++ b/drivers/crypto/ccp/ccp-dmaengine.c
> @@ -641,6 +641,10 @@ static void ccp_dma_release(struct ccp_device *ccp)
>   	for (i = 0; i < ccp->cmd_q_count; i++) {
>   		chan = ccp->ccp_dma_chan + i;
>   		dma_chan = &chan->dma_chan;
> +
> +		if (dma_chan->client_count)
> +			dma_release_channel(dma_chan);
> +
>   		tasklet_kill(&chan->cleanup_tasklet);
>   		list_del_rcu(&dma_chan->device_node);
>   	}
> @@ -762,12 +766,14 @@ int ccp_dmaengine_register(struct ccp_device *ccp)
>   void ccp_dmaengine_unregister(struct ccp_device *ccp)
>   {
>   	struct dma_device *dma_dev = &ccp->dma_dev;
> +	struct dma_chan *dma_chan;
> +	unsigned int i;
>   
>   	if (!dmaengine)
>   		return;
>   
> -	dma_async_device_unregister(dma_dev);
>   	ccp_dma_release(ccp);
> +	dma_async_device_unregister(dma_dev);

Seems the right way to get rid of the warn, but can there still be a race 
where the channel is grabbed again after ccp_dma_release() and before 
dma_async_device_unregister() is called?

Thanks,
Tom

>   
>   	kmem_cache_destroy(ccp->dma_desc_cache);
>   	kmem_cache_destroy(ccp->dma_cmd_cache);