Subject: Re: [PATCH] net/usb: rtl8150: allocate URB transfer_buffer and setup_packet separately

From: Jussi Kivilinna <[email-masked]>
Date: Sat, 10 Aug 2013 10:38:19 +0300

On 09.08.2013 21:50, Petko Manolov wrote:
> On Thu, 8 Aug 2013, Jussi Kivilinna wrote:
> 
>> On 08.08.2013 18:14, Petko Manolov wrote:
>>> On Wed, 7 Aug 2013, Jussi Kivilinna wrote:
>>>
>>>> rtl8150 allocates URB transfer_buffer and setup_packet as part of same 
>>>> structure 'struct async_req'. This can cause same cacheline to be 
>>>> DMA-mapped twice with same URB. This can lead to memory corruption on 
>>>> some systems.
>>>
>>> I can see performance impact due to the double mapping.  However, memory 
>>> corruption seems a bit too much for sane cache and DMA controllers.  Out 
>>> of interest - which is the architecture that will potentially corrupt the 
>>> memory.
>>
>> rtlwifi driver had similar structure to allocate both setup_packet and 
>> transfer_buffer in single go (overlapping dma-mapping cachelines) and 
>> this caused problems on ARM/sunxi. Problems means: memory corruptions at 
>> random locations, device freezes and lock-ups.
> 
> Broken controllers?..
> 

At first I thought so too, but I discussed about this at linux-usb, and answer
was that driver which uses same (dma/-)cacheline for multiple buffers is buggy..
  http://marc.info/?l=linux-usb&m=137130407121137&w=2 (at end)
  http://marc.info/?l=linux-usb&m=137137080902265&w=2
  http://marc.info/?l=linux-usb&m=137242422120782&w=2

-Jussi