Subject: Re: [PATCH V2 00/11] Subject: Remove duplicated kmap code

From: Al Viro <[email-masked]>
Date: Mon, 4 May 2020 22:02:25 +0100

On Mon, May 04, 2020 at 01:17:41PM -0700, Ira Weiny wrote:

> > || * arm: much, much worse.  We have several files that pull linux/highmem.h:
> > || arch/arm/mm/cache-feroceon-l2.c, arch/arm/mm/cache-xsc3l2.c,
> > || arch/arm/mm/copypage-*.c, arch/arm/mm/dma-mapping.c, arch/arm/mm/flush.c,
> > || arch/arm/mm/highmem.c, arch/arm/probes/uprobes/core.c,
> > || arch/arm/include/asm/kvm_mmu.h (kmap_atomic_pfn()).
> > || Those are fine, but we also have this:
> > || arch/arm/include/asm/pgtable.h:200:#define __pte_map(pmd)               (pte_t *)kmap_atomic(pmd_page(*(pmd)))
> > || arch/arm/include/asm/pgtable.h:208:#define pte_offset_map(pmd,addr)     (__pte_map(pmd) + pte_index(addr))
> > || and sure as hell, asm/pgtable.h does *NOT* pull linux/highmem.h.
> 
> It does not pull asm/highmem.h either...

No, but the users of those macros need to be considered.

> > || #define pte_offset_map(dir, addr)               \
> > ||         ((pte_t *) kmap_atomic(pmd_page(*(dir))) + pte_index(addr))
> > ||         One pte_offset_map user in arch/microblaze:
> > || arch/microblaze/kernel/signal.c:207:    ptep = pte_offset_map(pmdp, address);
> > || Messy, but doesn't require any changes (we have asm/pgalloc.h included
> > || there, and that pull linux/highmem.h).
> 
> AFAICS asm/pgtable.h does not include asm/highmem.h here...
> 
> So looks like arch/microblaze/kernel/signal.c will need linux/highmem.h

See above - line 39 in there is
#include <asm/pgalloc.h>
and line 14 in arch/microblaze/include/asm/pgalloc.h is
#include <linux/highmem.h>
It's conditional upon CONFIG_MMU in there, but so's the use of
pte_offset_map() in arch/microblaze/kernel/signal.c 

So it shouldn't be a problem.

> > || * xtensa: users in arch/xtensa/kernel/pci-dma.c, arch/xtensa/mm/highmem.c,
> > || arch/xtensa/mm/cache.c and arch/xtensa/platforms/iss/simdisk.c (all pull
> > || linux/highmem.h).
> 
> Actually
> 
> arch/xtensa/mm/cache.c gets linux/highmem.h from linux/pagemap.h
> 
> arch/xtensa/platforms/iss/simdisk.c may have an issue?
> 	linux/blkdev.h -> CONFIG_BLOCK -> linux/pagemap.h -> linux/highmem.h
> 	But simdisk.c requires BLK_DEV_SIMDISK -> CONFIG_BLOCK...
> 	<sigh>

Yep - see above re major chain of indirect includes conditional upon CONFIG_BLOCK
and its uses in places that only build with such configs.  There's a plenty of
similar considerations outside of arch/*, unfortunately...