linux-kernel - Re: [PATCH 3/3] dmaengine: Fix client_count is countered one more incorrectly.

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Date:   Fri, 2 Sep 2022 15:13:58 +0800
From:   Jie Hai <haijie1@...wei.com>
To:     Koba Ko <koba.ko@...onical.com>, Vinod Koul <vkoul@...nel.org>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] dmaengine: Fix client_count is countered one more
 incorrectly.

Hi, Koba Ko

Thanks for your patch.

I've had the same problem,see
https://lore.kernel.org/all/20220716024453.1418259-1-haijie1@huawei.com/.

The two operations of updating client_count, that is,
     chan->client_count++;
     balance_ref_count(chan);

the order of which is modified by d2f4f99db3e9 ("dmaengine: Rework 
dma_chan_get").

I have complied and tested it on my arm64 and this patch does
fix the problem.

For this patch,
Reviewed-by: Jie Hai <haijie1@...wei.com>
Test-by: Jie Hai <haijie1@...wei.com>

Best regards,
Jie Hai

On 2022/8/30 17:32, Koba Ko wrote:
> If the passed client_count is 0,
> it would be incremented by balance_ref_count first
> then increment one more.
> This would cause client_count to 2.
> 
> cat /sys/class/dma/dma0chan*/in_use
> 2
> 2
> 2
> 
> Fixes: d2f4f99db3e9 ("dmaengine: Rework dma_chan_get")
> Signed-off-by: Koba Ko <koba.ko@...onical.com>
> ---
>   drivers/dma/dmaengine.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 2cfa8458b51be..78f8a9f3ad825 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -451,7 +451,8 @@ static int dma_chan_get(struct dma_chan *chan)
>   	/* The channel is already in use, update client count */
>   	if (chan->client_count) {
>   		__module_get(owner);
> -		goto out;
> +		chan->client_count++;
> +		return 0;
>   	}
>   
>   	if (!try_module_get(owner))
> @@ -470,11 +471,11 @@ static int dma_chan_get(struct dma_chan *chan)
>   			goto err_out;
>   	}
>   
> +	chan->client_count++;
> +
>   	if (!dma_has_cap(DMA_PRIVATE, chan->device->cap_mask))
>   		balance_ref_count(chan);
>   
> -out:
> -	chan->client_count++;
>   	return 0;
>   
>   err_out: