Re: [dm-devel] [PATCH v2] qat: fix deadlock in backlog processing

[Mikulas Patocka <mpatocka@redhat.com>]

On Fri, 29 Sep 2023, Giovanni Cabiddu wrote:

> On Fri, Sep 22, 2023 at 06:34:16PM +0200, Mikulas Patocka wrote:
> >
> > > Also, deserves a fixes tag.
> > 
> > "Fixes" tag is for something that worked and that was broken in some 
> > previous commit.
> That's right.
> 
> > A quick search through git shows that QAT backlogging was 
> > broken since the introduction of QAT.
> The driver was moved from drivers/crypto/qat to drivers/crypto/intel/qat
> that's why you see a single patch.
> This fixes 386823839732 ("crypto: qat - add backlog mechanism")

But before 386823839732 it also didn't work - it returned -EBUSY without 
queuing the request and deadlocked.

> Thanks - when I proposed the rework I was thinking at a solution without
> gotos. Here is a draft:

Yes - it is possible to fix it this way.



> ------------8<----------------
>  .../intel/qat/qat_common/qat_algs_send.c      | 40 ++++++++++---------
>  1 file changed, 22 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/crypto/intel/qat/qat_common/qat_algs_send.c b/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
> index bb80455b3e81..18c6a233ab96 100644
> --- a/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
> +++ b/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
> @@ -40,17 +40,7 @@ void qat_alg_send_backlog(struct qat_instance_backlog *backlog)
>  	spin_unlock_bh(&backlog->lock);
>  }
>  
> -static void qat_alg_backlog_req(struct qat_alg_req *req,
> -				struct qat_instance_backlog *backlog)
> -{
> -	INIT_LIST_HEAD(&req->list);
> -
> -	spin_lock_bh(&backlog->lock);
> -	list_add_tail(&req->list, &backlog->list);
> -	spin_unlock_bh(&backlog->lock);
> -}
> -
> -static int qat_alg_send_message_maybacklog(struct qat_alg_req *req)
> +static bool qat_alg_try_enqueue(struct qat_alg_req *req)
>  {
>  	struct qat_instance_backlog *backlog = req->backlog;
>  	struct adf_etr_ring_data *tx_ring = req->tx_ring;
> @@ -58,22 +48,36 @@ static int qat_alg_send_message_maybacklog(struct qat_alg_req *req)
>  
>  	/* If any request is already backlogged, then add to backlog list */
>  	if (!list_empty(&backlog->list))
> -		goto enqueue;
> +		return false;
>  
>  	/* If ring is nearly full, then add to backlog list */
>  	if (adf_ring_nearly_full(tx_ring))
> -		goto enqueue;
> +		return false;
>  
>  	/* If adding request to HW ring fails, then add to backlog list */
>  	if (adf_send_message(tx_ring, fw_req))
> -		goto enqueue;
> +		return false;
>  
> -	return -EINPROGRESS;
> +	return true;
> +}
>  
> -enqueue:
> -	qat_alg_backlog_req(req, backlog);
>  
> -	return -EBUSY;
> +static int qat_alg_send_message_maybacklog(struct qat_alg_req *req)
> +{
> +	struct qat_instance_backlog *backlog = req->backlog;
> +	int ret = -EINPROGRESS;
> +
> +	if (qat_alg_try_enqueue(req))
> +		return ret;
> +
> +	spin_lock_bh(&backlog->lock);
> +	if (!qat_alg_try_enqueue(req)) {
> +		list_add_tail(&req->list, &backlog->list);
> +		ret = -EBUSY;
> +	}
> +	spin_unlock_bh(&backlog->lock);
> +
> +	return ret;
>  }
>  
>  int qat_alg_send_message(struct qat_alg_req *req)
> -- 
> 2.41.0


Reviwed-by: Mikulas Patocka <mpatocka@redhat.com>

Mikulas


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