Re: i386: selftests: vm: compaction_test: BUG: kernel NULL pointer dereference, address: 00000000

[Peter Xu]

On Mon, Apr 13, 2020 at 04:51:25PM +0530, Naresh Kamboju wrote:
> On Mon, 13 Apr 2020 at 03:12, Peter Xu <peterx@xxxxxxxxxx> wrote:
> > And since this one is very easy to reproduce, I finally noticed that
> > we have wrongly enabled uffd-wp on x86_32, which is definely not going
> > to work... Because we'll use bit 2 of swap entry assuming that's the
> > uffd-wp bit, while that's part of swp offset on 32bit systems.
> >
> > Naresh, could you try whether below change fixes the issue for you?
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 8d078642b4be..7ac524d1316e 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -149,7 +149,7 @@ config X86
> >         select HAVE_ARCH_TRACEHOOK
> >         select HAVE_ARCH_TRANSPARENT_HUGEPAGE
> >         select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
> > -       select HAVE_ARCH_USERFAULTFD_WP         if USERFAULTFD
> > +       select HAVE_ARCH_USERFAULTFD_WP         if X86_64 && USERFAULTFD
> >         select HAVE_ARCH_VMAP_STACK             if X86_64
> >         select HAVE_ARCH_WITHIN_STACK_FRAMES
> >         select HAVE_ASM_MODVERSIONS
> >
> 
> Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
> 
> The above patch tested and did not notice the crash.
> + cd /opt/kselftests/default-in-kernel/vm/
> + ./compaction_test
> No of huge pages allocated = 297
> + ./compaction_test
> [   46.059785] kauditd_printk_skb: 15 callbacks suppressed
> [   46.059786] audit: type=1334 audit(1586776582.927:25): prog-id=17 op=UNLOAD
> [   46.071997] audit: type=1334 audit(1586776582.927:26): prog-id=16 op=UNLOAD
> No of huge pages allocated = 160
> 
> Full test log,
> https://lkft.validation.linaro.org/scheduler/job/1362495#L1308
> 
> Build artifacts.
> https://builds.tuxbuild.com/w0ol7cCsGan0wzPp7bNqkg/

Thanks!  I'll post a formal patch soon.

-- 
Peter Xu