linux-kernel - Re: [PATCH] soc: ti: k3-ringacc: Add try_module_get() to k3_dmaring_request_dual

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Date:   Sun, 25 Dec 2022 00:03:38 +0200
From:   Péter Ujfalusi <peter.ujfalusi@...il.com>
To:     Nicolas Frayer <nfrayer@...libre.com>, nm@...com,
        ssantosh@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        grygorii.strashko@...com, khilman@...libre.com,
        mkorpershoek@...libre.com
Subject: Re: [PATCH] soc: ti: k3-ringacc: Add try_module_get() to
 k3_dmaring_request_dual_ring()

Hi Nicolas,

On 21/12/2022 22:05, Nicolas Frayer wrote:
> When the k3 ring accelerator driver has been modified to add module build
> support, try_module_get() and module_put() have been added to update the
> module refcnt. One code path has not been updated and it has introduced
> an issue where the refcnt is decremented by module_put() in
> k3_ringacc_ring_free() without being incremented previously.
> Adding try_module_get() to k3_dmaring_request_dual_ring() ensures the
> refcnt is kept up to date.

Good catch!
I had never had my hands on a device with DMSS (BCDMA/PKDMA) and the
original module support was developed and tested on devices with UDMA.

can you add the fixes tag along with my reviewed by tag?

Fixes: c07f216a8b72 ("soc: ti: k3-ringacc: Allow the driver to be built as module")
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@...il.com>

> 
> Signed-off-by: Nicolas Frayer <nfrayer@...libre.com>
> ---
>   drivers/soc/ti/k3-ringacc.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/soc/ti/k3-ringacc.c b/drivers/soc/ti/k3-ringacc.c
> index e01e4d815230a..8f131368a7586 100644
> --- a/drivers/soc/ti/k3-ringacc.c
> +++ b/drivers/soc/ti/k3-ringacc.c
> @@ -406,6 +406,11 @@ static int k3_dmaring_request_dual_ring(struct k3_ringacc *ringacc, int fwd_id,
>   
>   	mutex_lock(&ringacc->req_lock);
>   
> +	if (!try_module_get(ringacc->dev->driver->owner)) {
> +		ret = -EINVAL;
> +		goto err_module_get;
> +	}
> +
>   	if (test_bit(fwd_id, ringacc->rings_inuse)) {
>   		ret = -EBUSY;
>   		goto error;
> @@ -421,6 +426,8 @@ static int k3_dmaring_request_dual_ring(struct k3_ringacc *ringacc, int fwd_id,
>   	return 0;
>   
>   error:
> +	module_put(ringacc->dev->driver->owner);
> +err_module_get:
>   	mutex_unlock(&ringacc->req_lock);
>   	return ret;
>   }

-- 
Péter