Re: [PATCH] page flags: prioritize kasan bits over last-cpuid

[Guenter Roeck <linux@roeck-us.net>]

On Mon, Aug 05, 2019 at 08:35:40PM +0200, Arnd Bergmann wrote:
> On Mon, Aug 5, 2019 at 6:51 PM Guenter Roeck <linux@roeck-us.net> wrote:
> >
> > On Fri, Aug 02, 2019 at 09:49:02PM -0700, Arnd Bergmann wrote:
> > > ARM64 randdconfig builds regularly run into a build error, especially
> > > when NUMA_BALANCING and SPARSEMEM are enabled but not SPARSEMEM_VMEMMAP:
> > >
> > >   #error "KASAN: not enough bits in page flags for tag"
> > >
> > > The last-cpuid bits are already contitional on the available space, so
> > > the result of the calculation is a bit random on whether they were
> > > already left out or not.
> > >
> > > Adding the kasan tag bits before last-cpuid makes it much more likely to
> > > end up with a successful build here, and should be reliable for
> > > randconfig at least, as long as that does not randomize NR_CPUS or
> > > NODES_SHIFT but uses the defaults.
> > >
> > > In order for the modified check to not trigger in the x86 vdso32 code
> > > where all constants are wrong (building with -m32), enclose all the
> > > definitions with an #ifdef.
> > >
> >
> > This results in
> >
> > ./include/linux/page-flags-layout.h:95:2: error: #error "Not enough bits in page flags"
> >  #error "Not enough bits in page flags"
> >
> > when trying to build mipsel64:fuloong2e_defconfig.
> 
> Do you have my follow-up fix applied?
> 
> https://ozlabs.org/~akpm/mmots/broken-out/page-flags-prioritize-kasan-bits-over-last-cpuid-fix.patch
> 

No. I see the failure in next-20190729..next-20190805.

I didn't try to apply that patch, but I don't see
arch/mips/vdso/vdso.h in the tree. I only see

arch/mips/include/asm/vdso.h
arch/mips/include/asm/vdso/vdso.h

Are you sure that your patch can be applied as-is ?

Guenter