Re: [PATCH v7 3/5] usb: host: ohci-sm501: init genalloc for local memory

From: Guenter Roeck <linux@roeck-us.net>
To: Fredrik Noring <noring@nocrew.org>
Cc: laurentiu.tudor@nxp.com, hch@lst.de, stern@rowland.harvard.edu,
	gregkh@linuxfoundation.org, linux-usb@vger.kernel.org,
	marex@denx.de, leoyang.li@nxp.com, linux-kernel@vger.kernel.org,
	robin.murphy@arm.com, JuergenUrban@gmx.de
Subject: Re: [PATCH v7 3/5] usb: host: ohci-sm501: init genalloc for local memory
Date: Thu, 13 Jun 2019 11:05:42 -0700	[thread overview]
Message-ID: <3f2164cd-7655-b7cc-ec57-d8751886728c@roeck-us.net> (raw)
In-Reply-To: <20190613153414.GA909@sx9>

On 6/13/19 8:34 AM, Fredrik Noring wrote:
> Hi Guenter,
> 
>> Thanks for the confirmation. Do you see the problem only with the
>> ohci-sm501 driver or also with others ?
> 
> All are likely affected, but it depends, because I believe the problem is
> that the USB subsystem runs out of memory. Please try the attached patch!
> 
> The pool assumed 4096 byte page alignment for every allocation, which is
> excessive given that many requests are for 16 and 32 bytes. In the patch
> below, I have turned down the order to 5, which is good enough for the ED
> and TD structures of the OHCI, but not enough for the HCCA that needs 256
> byte alignment. With some luck, the WARN_ON_ONCE will not trigger in your
> test, though. If it does, you may try to increase the order from 5 to 8.
> 

You are right, the patch below fixes the problem. I did not get the warning
with order==5. Nevertheless, I also tested with order==8; that works as well.

Thanks a lot for tracking this down!
Guenter

> I have observed strange things happen when the USB subsystem runs out of
> memory. The mass storage drivers often seem to busy-wait on -ENOMEM,
> consuming a lot of processor resources. It would be much more efficient
> to sleep waiting for memory to become available.
> 
> In your case I suspect that allocation failures are not correctly
> attributed. Certain kinds of temporary freezes may also occur, as the
> various devices are reset due to host memory allocation errors.
>  > Fredrik
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -3011,7 +3011,7 @@ int usb_hcd_setup_local_mem(struct usb_hcd *hcd, phys_addr_t phys_addr,
>   	int err;
>   	void __iomem *local_mem;
>   
> -	hcd->localmem_pool = devm_gen_pool_create(hcd->self.sysdev, PAGE_SHIFT,
> +	hcd->localmem_pool = devm_gen_pool_create(hcd->self.sysdev, 5,
>   						  dev_to_node(hcd->self.sysdev),
>   						  dev_name(hcd->self.sysdev));
>   	if (IS_ERR(hcd->localmem_pool))
> diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
> --- a/drivers/usb/host/ohci-hcd.c
> +++ b/drivers/usb/host/ohci-hcd.c
> @@ -517,6 +517,7 @@ static int ohci_init (struct ohci_hcd *ohci)
>   						GFP_KERNEL);
>   	if (!ohci->hcca)
>   		return -ENOMEM;
> +	WARN_ON_ONCE(ohci->hcca_dma & 0xff);
>   
>   	if ((ret = ohci_mem_init (ohci)) < 0)
>   		ohci_stop (hcd);
> 