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

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Date:   Mon, 5 Aug 2019 20:35:40 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] page flags: prioritize kasan bits over last-cpuid

On Mon, Aug 5, 2019 at 6:51 PM Guenter Roeck <linux@...ck-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

       Arnd