netdev - Re: [PATCH 2/7] net: ethernet: ti: cpsw: Don't error out in .remove()

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Date: Sat, 18 Nov 2023 12:00:08 +0200
From: Roger Quadros <rogerq@...nel.org>
To: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: Siddharth Vadapalli <s-vadapalli@...com>,
 Ravi Gunasekaran <r-gunasekaran@...com>, Simon Horman <horms@...nel.org>,
 Yunsheng Lin <linyunsheng@...wei.com>, Stanislav Fomichev <sdf@...gle.com>,
 Marek Majtyka <alardam@...il.com>, Rob Herring <robh@...nel.org>,
 Mugunthan V N <mugunthanvnm@...com>, linux-omap@...r.kernel.org,
 netdev@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH 2/7] net: ethernet: ti: cpsw: Don't error out in .remove()



On 17/11/2023 11:16, Uwe Kleine-König wrote:
> Returning early from .remove() with an error code still results in the
> driver unbinding the device. So the driver core ignores the returned error
> code and the resources that were not freed are never catched up. In
> combination with devm this also often results in use-after-free bugs.
> 
> If runtime resume fails, it's still important to free all resources, so
> don't return with an error code, but emit an error message and continue
> freeing acquired stuff.
> 
> This prepares changing cpsw_remove() to return void.
> 
> Fixes: 8a0b6dc958fd ("drivers: net: cpsw: fix wrong regs access in cpsw_remove")
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> ---
>  drivers/net/ethernet/ti/cpsw.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ti/cpsw.c b/drivers/net/ethernet/ti/cpsw.c
> index ca4d4548f85e..db5a2ba8a6d4 100644
> --- a/drivers/net/ethernet/ti/cpsw.c
> +++ b/drivers/net/ethernet/ti/cpsw.c
> @@ -1727,16 +1727,24 @@ static int cpsw_remove(struct platform_device *pdev)
>  	struct cpsw_common *cpsw = platform_get_drvdata(pdev);
>  	int i, ret;
>  
> -	ret = pm_runtime_resume_and_get(&pdev->dev);
> +	ret = pm_runtime_get_sync(&pdev->dev);
>  	if (ret < 0)
> -		return ret;
> +		/* There is no need to do something about that. The important
> +		 * thing is to not exit early, but do all cleanup that doesn't
> +		 * require register access.
> +		 */
> +		dev_err(&pdev->dev, "runtime resume failed (%pe)\n",
> +			ERR_PTR(ret));
>  
>  	for (i = 0; i < cpsw->data.slaves; i++)
>  		if (cpsw->slaves[i].ndev)
>  			unregister_netdev(cpsw->slaves[i].ndev);
>  
> -	cpts_release(cpsw->cpts);
> -	cpdma_ctlr_destroy(cpsw->dma);
> +	if (ret >= 0) {
> +		cpts_release(cpsw->cpts);

cpts_release() only does clk_unprepare().
Why not do that in the error path as well?

> +		cpdma_ctlr_destroy(cpsw->dma);

cpdma_ctrl_destroy() not only stops the DMA controller
but also frees up the channel and calls dma_free_coherent?

We still want to free up the channel and dma_free_coherent in the
error path?

> +	}
> +
>  	cpsw_remove_dt(pdev);
>  	pm_runtime_put_sync(&pdev->dev);
>  	pm_runtime_disable(&pdev->dev);

-- 
cheers,
-roger