[LEDE-DEV] MMAP memory out of sync on AR71xx Rambutan (8devices) board.

[Daniel Danzberger]

On 05/07/2018 01:16 PM, Daniel Danzberger wrote:
> On 05/06/2018 09:00 PM, Rosen Penev wrote:
>> On Sun, May 6, 2018 at 10:08 AM, Rosen Penev <rosenp at gmail.com> wrote:
>>> On Sun, May 6, 2018 at 3:52 AM, Daniel Danzberger <daniel at dd-wrt.com> wrote:
>>>> MMAP'ed memory that has been allocated via 'get_zeroed_page(GFP_KERNEL)' or
>>>> 'vmalloc()' doesn't always contain the same data when accessed from userspace.
>>>>
>>>> This means all userspace programs using mmap to access kernel memory aren't
>>>> always working properly on the Rambutan board. I am currently testing if other
>>>> ar71xx devices are affected as well.
>>>>
>>>> I first noticed this when using ALSA's mmap api to capture audio.
>>>>
>>>> Here is the feed for a kmod + userpace util to reproduce the issue:
>>>> git at github.com:dddaniel/mmaptest.git
>>>>
>>>> The kernel module simply allocates a page and initializes it with 0xff.
>>>> The userspace application then mmap's and reads this page 10 times with a 500ms
>>>> delay an checks if all data is 0xff.
>>>>
>>>> ---
>>>> root at OpenWrt:/# mmaptest-user
>>>> mmap addr: 0x77a04000
>>>> [  760.464968] mmap page 7573000 at va 87573000
>>>> check memory ...FAIL (at byte 0)
>>>> check memory ...FAIL (at byte 96)
>>>> check memory ...FAIL (at byte 96)
>>>> check memory ...FAIL (at byte 96)
>>>> check memory ...FAIL (at byte 128)
>>>> ---
>>>>
>>>> I have no idea whats causing it. Does anybody have a hint on how to fix this ?
>>>>
>>> Try reverting https://github.com/torvalds/linux/commit/c00ab4896ed5f7d89af6f90b809e2c0197c6d170
>> Disregard that. That commit should have no impact.
>>
>> I just tested it on an Archer C7v4 and the issue is present as well.
>> This was probably causing data corruption for me when I used an
>> external hard drive...
>>
>> Strange that sometimes it works and sometimes not.Yes, the same in my tests. Look's like this issue appears on all ar71xx devices.
>>
>> Did you encounter this issue with kernel 4.9? For me, 4.4 caused no
>> data corruption on my external hard drive.
> I can't tell right now. I was trying to use an older version with kernel 4.4,
> but it fails to build.
I just tested with 4.4 and the problem is present there as well.
>>
>> There seems to be a pattern with kernel 4.9 breaking various MIPS devices...
> 
>>>> --
>>>> Regards
>>>>
>>>> Daniel Danzberger
>>>> embeDD GmbH, Alter Postplatz 2, CH-6370 Stans
>>>>
>>>> _______________________________________________
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>>>> Lede-dev at lists.infradead.org
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>>
> 

-- 
Regards

Daniel Danzberger
embeDD GmbH, Alter Postplatz 2, CH-6370 Stans