On Tue, Nov 22, 2022 at 2:55 AM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> Hi, Anatoly (or/and Hev),
>
> On Wed, Nov 16, 2022 at 01:45:15PM +0300, Anatoly Pugachev wrote:
> > On Wed, Nov 16, 2022 at 11:49 AM hev <r@xxxxxx> 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
> > ...
>
> I've got another patch attached that might be nicer to fix this same
> problem for both archs but without dropping the dirty bit, could you help
> check whether it works?
The tesecase PASSED with this patch and without:
* "Partly revert "mm/thp: carry over dirty bit when thp splits on pmd"
* "LoongArch: Set _PAGE_DIRTY only if _PAGE_WRITE is set in
{pmd,pte}_mkdirty()"
Ray
