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

[Daniel Danzberger]

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.
> 
> 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
>>>
>>> _______________________________________________
>>> Lede-dev mailing list
>>> Lede-dev at lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/lede-dev
> 

-- 
Regards

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