linux-kernel - Re: [PATCH v2] mtd: rawnand: atmel: fix refcount issue in atmel_nand_controller

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Date:   Tue, 1 Mar 2022 09:50:37 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Xin Xiong <xiongx18@...an.edu.cn>
Cc:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        linux-mtd@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        yuanxzhang@...an.edu.cn, Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH v2] mtd: rawnand: atmel: fix refcount issue in
 atmel_nand_controller_init

On Tue,  1 Mar 2022 12:45:56 +0800
Xin Xiong <xiongx18@...an.edu.cn> wrote:

> The reference counting issue happens in several error handling paths
> on a refcounted object "nc->dmac". In these paths, the function simply
> returns the error code, forgetting to balance the reference count of
> "nc->dmac", increased earlier by dma_request_channel(), which may
> cause refcount leaks.
> 
> Fix it by decrementing the refcount of specific object in those error
> paths.
> 
> Fixes: f88fc122cc34 ("mtd: nand: Cleanup/rework the atmel_nand driver")
> Co-developed-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Co-developed-by: Xin Tan <tanxin.ctf@...il.com>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
> Signed-off-by: Xin Xiong <xiongx18@...an.edu.cn>
> ---
> V1 -> V2: Rewrited the error handling block
> ---
>  drivers/mtd/nand/raw/atmel/nand-controller.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/atmel/nand-controller.c b/drivers/mtd/nand/raw/atmel/nand-controller.c
> index f3276ee9e4fe..0efeb5d77be0 100644
> --- a/drivers/mtd/nand/raw/atmel/nand-controller.c
> +++ b/drivers/mtd/nand/raw/atmel/nand-controller.c
> @@ -2060,13 +2060,15 @@ static int atmel_nand_controller_init(struct atmel_nand_controller *nc,
>  	nc->mck = of_clk_get(dev->parent->of_node, 0);
>  	if (IS_ERR(nc->mck)) {
>  		dev_err(dev, "Failed to retrieve MCK clk\n");
> -		return PTR_ERR(nc->mck);
> +		ret = PTR_ERR(nc->mck);
> +		goto out_release_dma;
>  	}
>  
>  	np = of_parse_phandle(dev->parent->of_node, "atmel,smc", 0);
>  	if (!np) {
>  		dev_err(dev, "Missing or invalid atmel,smc property\n");
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		goto out_release_dma;
>  	}
>  
>  	nc->smc = syscon_node_to_regmap(np);
> @@ -2074,10 +2076,20 @@ static int atmel_nand_controller_init(struct atmel_nand_controller *nc,
>  	if (IS_ERR(nc->smc)) {
>  		ret = PTR_ERR(nc->smc);
>  		dev_err(dev, "Could not get SMC regmap (err = %d)\n", ret);
> -		return ret;
> +		goto out_release_dma;
>  	}
>  
>  	return 0;
> +
> +out_release_dma:
> +	if (nc->caps->has_dma && !atmel_nand_avoid_dma) {
> +		if (nc->dmac) {
> +			dma_release_channel(nc->dmac);
> +			nc->dmac = NULL;
> +		}
> +	}

Nit:

	if (nc->dmac)
		dma_release_channel(nc->dmac);

should work just fine.

> +
> +	return ret;
>  }
>  
>  static int