Re: 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@xxxxxxxxxxxxx>
---
  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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