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SubjectRe: crypto: ccp - Release dma channels before dmaengine unrgister
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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);

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