linux-kernel - Re: d451564 breakage

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Message-Id: <20091113115429.94e0885b.akpm@linux-foundation.org>
Date:	Fri, 13 Nov 2009 11:54:29 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Russell King <rmk@....linux.org.uk>
Cc:	Soeren Sandmann Pedersen <sandmann@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: d451564 breakage

On Fri, 13 Nov 2009 15:11:19 +0000
Russell King <rmk@....linux.org.uk> wrote:

> Change:
> 
> highmem: Fix debug_kmap_atomic() to also handle KM_IRQ_PTE, KM_NMI, and KM_NMI_PTE
> 
> Appears to break ARM:
> 
> mm/highmem.c: In function ___debug_kmap_atomic___:
> mm/highmem.c:436: error: ___KM_NMI___ undeclared (first use in this function)
> mm/highmem.c:436: error: (Each undeclared identifier is reported only once
> mm/highmem.c:436: error: for each function it appears in.)
> mm/highmem.c:436: error: ___KM_NMI_PTE___ undeclared (first use in this function)
> mm/highmem.c:443: error: ___KM_IRQ_PTE___ undeclared (first use in this function)
> make[2]: *** [mm/highmem.o] Error 1
> make[1]: *** [mm] Error 2
> 
> I'd prefer not to have to add these definitions just so that highmem
> debugging can work for two reasons:
> 
> 1. either we allocate mappings for these which will never be used, which
>    unnecessarily wastes precious virtual memory space.
> 
> 2. we define them to be some other KM_* value and hope that they never
>    get used.  If they do get used, we'll never know by way of compiler
>    error but could result in silent data corruption.
> 
> The only sane alternative I can see would be to define these as KM_TYPE_NR
> and either ensure that kmap_atomic() always fails for out-of-bounds kmap
> types (more preferable to catch problems but has a performance impact) or
> we have the kmap debugging detect this as well.
> 
> Any preferences?

Could we do something nasty with ifdefs?

In arch header:
#define KM_NMI KM_NMI


In generic code:
#ifdef KM_NMI
	<stuff which references KM_NMI>
#endif

or similar?
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