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@xxxxxxxxxx>
> ---
> 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
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