Re: [PATCH V1 09/10] arch/kmap: Define kmap_atomic_prot() for all arch's

[Al Viro]

On Fri, May 01, 2020 at 03:37:34AM +0100, Al Viro wrote:
> On Thu, Apr 30, 2020 at 01:38:44PM -0700, ira.weiny@xxxxxxxxx wrote:
> 
> > -static inline void *kmap_atomic(struct page *page)
> > +static inline void *kmap_atomic_prot(struct page *page, pgprot_t prot)
> >  {
> >  	preempt_disable();
> >  	pagefault_disable();
> >  	if (!PageHighMem(page))
> >  		return page_address(page);
> > -	return kmap_atomic_high(page);
> > +	return kmap_atomic_high_prot(page, prot);
> >  }
> > +#define kmap_atomic(page)	kmap_atomic_prot(page, kmap_prot)
> 
> OK, so it *was* just a bisect hazard - you return to original semantics
> wrt preempt_disable()...

FWIW, how about doing the following: just before #5/10 have a patch
that would touch only microblaze, ppc and x86 splitting their
kmap_atomic_prot() into an inline helper + kmap_atomic_high_prot().
Then your #5 would leave their kmap_atomic_prot() as-is (it would
use kmap_atomic_prot_high() instead).  The rest of the series plays
out pretty much the same way it does now, and wrappers on those
3 architectures would go away when an identical generic one is
introduced in this commit (#9/10).

AFAICS, that would avoid the bisect hazard and might even end
up with less noise in the patches...