Re: Crash in MM code in v4.4.y, v4.9.y with TRANSPARENT_HUGEPAGE enabled

[Guenter Roeck]

On Mon, Aug 20, 2018 at 01:18:43PM -0700, Andi Kleen wrote:
> On Mon, Aug 20, 2018 at 11:03:53AM -0700, Andi Kleen wrote:
> > On Mon, Aug 20, 2018 at 06:29:38PM +0200, Michal Hocko wrote:
> > > On Fri 17-08-18 15:27:33, Guenter Roeck wrote:
> > > > Hi,
> > > > 
> > > > the following crash is seen in v4.4.148, v4.4.149, v4.9.120, and v4.9.121
> > > > with CONFIG_TRANSPARENT_HUGEPAGE=y, CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y.
> > > 
> > > Could you try to apply fd7e315988b7 ("x86/mm: Simplify p[g4um]d_page()
> > > macros"). I do not see it in stable 4.4 tree and it has been introduced
> > > much later in 4.14. This one gave us quite some headache because it is
> > > soooo easy to overlook.
> > 
> > Good catch!
> > 
> > I tested that with 4.9 and backporting the patch indeed fixes the
> > syzcaller test case running in a KVM VM. Backported patch appended.
> 
> Tested on 4.4 too and it fixes the syzkaller test case there too.
> 

Confirmed that the problem is fixed in v4.4.151-rc1 and v4.9.123-rc1.

Thanks a lot for tracking this down and backporting the fix!

Guenter