linux-kernel - Re: [PATCH] dmaengine: device must have at least one channel

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Date:	Thu, 28 Jul 2016 09:18:43 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linaro-kernel@...ts.linaro.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: device must have at least one channel

On Wed, Jul 27, 2016 at 02:32:58PM -0700, Viresh Kumar wrote:
> The DMA device can't be registered if it doesn't have any channels
> registered at all. Moreover, it leads to memory leak and is reported by
> kmemleak as (on 3.10 kernel, and same shall happen on mainline):
> 
> unreferenced object 0xffffffc09e597240 (size 64):
>   comm "swapper/0", pid 1, jiffies 4294877736 (age 7060.280s)
>   hex dump (first 32 bytes):
>     00 00 00 00 c0 ff ff ff 30 00 00 ff 00 00 00 ff  ........0.......
>     00 00 00 ff 00 00 00 ff 00 00 00 ff 00 00 00 ff  ................
>   backtrace:
>     [<ffffffc0003079ec>] create_object+0x148/0x2a0
>     [<ffffffc000cc150c>] kmemleak_alloc+0x80/0xbc
>     [<ffffffc000303a7c>] kmem_cache_alloc_trace+0x120/0x1ac
>     [<ffffffc00054771c>] dma_async_device_register+0x160/0x46c
>     [<ffffffc000548958>] foo_probe+0x1a0/0x264
>     [<ffffffc0005d6658>] platform_drv_probe+0x14/0x20
>     [<ffffffc0005d50cc>] driver_probe_device+0x160/0x374
>     [<ffffffc0005d538c>] __driver_attach+0x60/0x90
>     [<ffffffc0005d3e78>] bus_for_each_dev+0x7c/0xb0
>     [<ffffffc0005d4a0c>] driver_attach+0x1c/0x28
>     [<ffffffc0005d459c>] bus_add_driver+0x124/0x248
>     [<ffffffc0005d59cc>] driver_register+0x90/0x110
>     [<ffffffc0005d6bf4>] platform_driver_register+0x58/0x64
>     [<ffffffc00142a70c>] foo_driver_init+0x10/0x1c
>     [<ffffffc000200878>] do_one_initcall+0xac/0x148
>     [<ffffffc00140096c>] kernel_init_freeable+0x1a0/0x258
> 
> Return -ENODEV from dma_async_device_register() on such a case.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> Hi Vinod,
> 
> Sorry if the fundamentals behind this patch are completely incorrect,
> i.e. We *can't* register a dma device with 0 channels. Its been long
> that I have worked on dma stuff :)

This sounds okay, but why would anyone register a device without having
a channel?

> 
>  drivers/dma/dmaengine.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 8c9f45fd55fc..6b535262ac5d 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -997,6 +997,13 @@ int dma_async_device_register(struct dma_device *device)
>  		}
>  		chan->client_count = 0;
>  	}
> +
> +	if (!chancnt) {
> +		dev_err(device->dev, "%s: device has no channels!\n", __func__);
> +		rc = -ENODEV;
> +		goto err_out;
> +	}
> +
>  	device->chancnt = chancnt;
>  
>  	mutex_lock(&dma_list_mutex);
> -- 
> 2.7.4
> 

-- 
~Vinod