Re: Test case for "mm/thp: carry over dirty bit when thp splits on pmd"

[Anatoly Pugachev <matorola@gmail.com>]

On Wed, Nov 16, 2022 at 11:49 AM hev <r@hev.cc> wrote:
>
> Hello Peter,
>
> I see a random crash issue  on the LoongArch system, that is caused by
> commit 0ccf7f1 ("mm/thp: carry over dirty bit when thp splits on
> pmd").
>
> Now, the thing is already resolved. The root cause is arch's mkdirty
> is set hardware writable bit in unconditional. That breaks
> write-protect and then breaks COW.
>
> Here is a simple and fast testcase (It may be helpful for sparc64):
> https://gist.github.com/heiher/72919fae6b53f04cac606a9631100506
> (assertion: c sum == 0)

Just tried on my sparc64 VM -  fixed vs old (non-patched) kernels...

fixed kernel (6.1.0-rc5) running ./a.out:
mator@ttip:~$ ./a.out
c sum: 0
p sum: 35184372088832
c sum: 0
p sum: 35184372088832
c sum: 0
p sum: 35184372088832
c sum: 0
p sum: 35184372088832
c sum: 0
p sum: 35184372088832
...

old (non-patched) kernel (6.1.0-rc4) :
mator@ttip:~$ ./a.out
c sum: 35150012350464
p sum: 35184372088832
c sum: 35150012350464
p sum: 35184372088832
...