Date:   Wed, 28 Mar 2018 15:06:38 +0000
From:   "Kani, Toshi" <toshi.kani@....com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "natechancellor@...il.com" <natechancellor@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "lious.lilei@...ilicon.com" <lious.lilei@...ilicon.com>,
        "dan.rue@...aro.org" <dan.rue@...aro.org>,
        "wxf.wang@...ilicon.com" <wxf.wang@...ilicon.com>,
        "guohanjun@...wei.com" <guohanjun@...wei.com>,
        "bp@...e.de" <bp@...e.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hpa@...or.com" <hpa@...or.com>,
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        "Hocko, Michal" <MHocko@...e.com>,
        "cpandya@...eaurora.org" <cpandya@...eaurora.org>,
        "willy@...radead.org" <willy@...radead.org>
Subject: Re: [PATCH 4.4 20/43] mm/vmalloc: add interfaces to free unmapped
 page table

On Wed, 2018-03-28 at 11:58 +0200, gregkh@...uxfoundation.org wrote:
> On Tue, Mar 27, 2018 at 11:47:18PM -0700, Nathan Chancellor wrote:
> > On Wed, Mar 28, 2018 at 08:32:02AM +0200, gregkh@...uxfoundation.org wrote:
> > > On Tue, Mar 27, 2018 at 01:47:55PM -0700, Nathan Chancellor wrote:
> > > > On Tue, Mar 27, 2018 at 08:40:56PM +0000, Kani, Toshi wrote:
> > > > > On Tue, 2018-03-27 at 13:31 -0700, Nathan Chancellor wrote:
> > > > > > On Tue, Mar 27, 2018 at 03:17:00PM -0500, Dan Rue wrote:
> > > > > > > On Tue, Mar 27, 2018 at 06:27:24PM +0200, Greg Kroah-Hartman wrote:
> > > > > > > > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > > > > > > > 
> > > > > 
> > > > >  :
> > > > > > > 
> > > > > > > This patch causes the following build error on 4.4 arm64:
> > > > > > > 
> > > > > > > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=build-arm64 defconfig
> > > > > > > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- O=build-arm64
> > > > > > > 
> > > > > > >   CC      arch/arm64/mm/mmu.o
> > > > > > > ../arch/arm64/mm/mmu.c:701:5: error: redefinition of ‘pud_free_pmd_page’
> > > > > > >  int pud_free_pmd_page(pud_t *pud)
> > > > > > >      ^~~~~~~~~~~~~~~~~
> > > > > > > In file included from ../arch/arm64/include/asm/pgtable.h:682:0,
> > > > > > >                  from ../include/linux/mm.h:55,
> > > > > > >                  from ../include/linux/mman.h:4,
> > > > > > >                  from ../arch/arm64/mm/mmu.c:25:
> > > > > > > ../include/asm-generic/pgtable.h:777:19: note: previous definition of ‘pud_free_pmd_page’ was here
> > > > > > >  static inline int pud_free_pmd_page(pud_t *pud)
> > > > > > >                    ^~~~~~~~~~~~~~~~~
> > > > > > > ../arch/arm64/mm/mmu.c:706:5: error: redefinition of ‘pmd_free_pte_page’
> > > > > > >  int pmd_free_pte_page(pmd_t *pmd)
> > > > > > >      ^~~~~~~~~~~~~~~~~
> > > > > > > In file included from ../arch/arm64/include/asm/pgtable.h:682:0,
> > > > > > >                  from ../include/linux/mm.h:55,
> > > > > > >                  from ../include/linux/mman.h:4,
> > > > > > >                  from ../arch/arm64/mm/mmu.c:25:
> > > > > > > ../include/asm-generic/pgtable.h:781:19: note: previous definition of ‘pmd_free_pte_page’ was here
> > > > > > >  static inline int pmd_free_pte_page(pmd_t *pmd)
> > > > > > >                    ^~~~~~~~~~~~~~~~~
> > > > > > > make[2]: *** [../scripts/Makefile.build:270: arch/arm64/mm/mmu.o] Error 1
> > > > > > > make[1]: *** [/home/drue/src/linux/4.4-rc/Makefile:969: arch/arm64/mm] Error 2
> > > > > > > make[1]: Leaving directory '/home/drue/src/linux/4.4-rc/build-arm64'
> > > > > > > make: *** [Makefile:152: sub-make] Error 2
> > > > > > > 
> > > > > > > 
> > > > > > 
> > > > > > Both of my arm64 devices built fine with this patch... It seems like
> > > > > > the only way to hit that error is if HAVE_ARCH_HUGE_VMAP isn't set,
> > > > > > which seems impossible since it is selected by ARM64...
> > > > > > 
> > > > > > Someone smarter than I might have more insight but this patch is
> > > > > > unchanged from upstream so I can only assume that this error would
> > > > > > manifest there as well.
> > > > > 
> > > > > It appears that HAVE_ARCH_HUGE_VMAP was introduced in 4.6 on arm64. 
> > > > > Hence the problem in 4.4.
> > > > > 
> > > > > Thanks,
> > > > > -Toshi
> > > > > 
> > > > 
> > > > Ah, thanks for the heads up, since I have 324420bf91f6 ("arm64: add
> > > > support for ioremap() block mappings") in my tree due to Linaro's
> > > > backport of it for their Linaro Stable Kernel, which serves as a base
> > > > for most Android kernels. My apologies for not digging deeper and sorry
> > > > for the noise!
> > > 
> > > So should I just drop this patch?
> > 
> > Unless I am reading the commit message wrong and ignoring the fact that
> > the mainling commit applied cleanly to 4.4.124, it seems like this is
> > still relevant for x86.
> > 
> > Toshi suggested dropping the changes to arch/arm64/mm/mmu.c, which won't
> > be a problem for arm64 devices running the stable kernels as they come
> > because they don't have HAVE_ARCH_HUGE_VMAP so they shouldn't be hitting
> > the bug mentioned in the commit message anyways.
> > 
> > However, for Android devices which have the mainline commit I mentioned
> > above introducing HAVE_ARCH_HUGE_VMAP, dropping those changes would mean
> > this commit isn't fixing the issue it mentions, which they would be able
> > to hit in theory.
> > 
> > I don't know how you want to handle that but a simple suggestion that
> > would not change the end result of the patch for both the stable tree
> > and frankenkernels would be to add a simple
> > 
> > #ifdef CONFIG_ARCH_HAVE_HUGE_VMAP
> > 
> > around the changes in arch/arm64/mm/mmu.c.

Agreed.

> > I'll let you be the final judge though! Cheers,
> 
> That's a good idea about the #ifdef, I've updated the patch to be like
> this, and pushed out a -rc2 with that change in it.

Great! Please note that Patch 4.4 21/43 applies on top of this 20/43
patch. 

Thanks!
-Toshi

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