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Commit 597781f3 authored by Cesar Eduardo Barros's avatar Cesar Eduardo Barros Committed by Linus Torvalds
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kmap_atomic: make kunmap_atomic() harder to misuse 

kunmap_atomic() is currently at level -4 on Rusty's "Hard To Misuse"
list[1] ("Follow common convention and you'll get it wrong"), except in
some architectures when CONFIG_DEBUG_HIGHMEM is set[2][3].

kunmap() takes a pointer to a struct page; kunmap_atomic(), however, takes
takes a pointer to within the page itself.  This seems to once in a while
trip people up (the convention they are following is the one from
kunmap()).

Make it much harder to misuse, by moving it to level 9 on Rusty's list[4]
("The compiler/linker won't let you get it wrong").  This is done by
refusing to build if the type of its first argument is a pointer to a
struct page.

The real kunmap_atomic() is renamed to kunmap_atomic_notypecheck()
(which is what you would call in case for some strange reason calling it
with a pointer to a struct page is not incorrect in your code).

The previous version of this patch was compile tested on x86-64.

[1] http://ozlabs.org/~rusty/index.cgi/tech/2008-04-01.html
[2] In these cases, it is at level 5, "Do it right or it will always
    break at runtime."
[3] At least mips and powerpc look very similar, and sparc also seems to
    share a common ancestor with both; there seems to be quite some
    degree of copy-and-paste coding here. The include/asm/highmem.h file
    for these three archs mention x86 CPUs at its top.
[4] http://ozlabs.org/~rusty/index.cgi/tech/2008-03-30.html


[5] As an aside, could someone tell me why mn10300 uses unsigned long as
    the first parameter of kunmap_atomic() instead of void *?

Signed-off-by: default avatarCesar Eduardo Barros <cesarb@cesarb.net>
Cc: Russell King <linux@arm.linux.org.uk> (arch/arm)
Cc: Ralf Baechle <ralf@linux-mips.org> (arch/mips)
Cc: David Howells <dhowells@redhat.com> (arch/frv, arch/mn10300)
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com> (arch/mn10300)
Cc: Kyle McMartin <kyle@mcmartin.ca> (arch/parisc)
Cc: Helge Deller <deller@gmx.de> (arch/parisc)
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org> (arch/parisc)
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> (arch/powerpc)
Cc: Paul Mackerras <paulus@samba.org> (arch/powerpc)
Cc: "David S. Miller" <davem@davemloft.net> (arch/sparc)
Cc: Thomas Gleixner <tglx@linutronix.de> (arch/x86)
Cc: Ingo Molnar <mingo@redhat.com> (arch/x86)
Cc: "H. Peter Anvin" <hpa@zytor.com> (arch/x86)
Cc: Arnd Bergmann <arnd@arndb.de> (include/asm-generic)
Cc: Rusty Russell <rusty@rustcorp.com.au> ("Hard To Misuse" list)
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3edd4fc9

arch/arm/include/asm/highmem.h

+1 −1
Original line number Diff line number Diff line
@@ -36,7 +36,7 @@ extern void kunmap_high_l1_vipt(struct page *page, pte_t saved_pte); 
extern void *kmap(struct page *page);

extern void kunmap(struct page *page);

extern void *kmap_atomic(struct page *page, enum km_type type);

extern void kunmap_atomic(void *kvaddr, enum km_type type);

extern void kunmap_atomic_notypecheck(void *kvaddr, enum km_type type);

extern void *kmap_atomic_pfn(unsigned long pfn, enum km_type type);

extern struct page *kmap_atomic_to_page(const void *ptr);

#endif

arch/arm/mm/highmem.c

+2 −2
Original line number Diff line number Diff line
@@ -82,7 +82,7 @@ void *kmap_atomic(struct page *page, enum km_type type) 
}

EXPORT_SYMBOL(kmap_atomic);



void kunmap_atomic(void *kvaddr, enum km_type type)

void kunmap_atomic_notypecheck(void *kvaddr, enum km_type type)

{

	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;

	unsigned int idx = type + KM_TYPE_NR * smp_processor_id();
@@ -103,7 +103,7 @@ void kunmap_atomic(void *kvaddr, enum km_type type) 
	}

	pagefault_enable();

}

EXPORT_SYMBOL(kunmap_atomic);

EXPORT_SYMBOL(kunmap_atomic_notypecheck);



void *kmap_atomic_pfn(unsigned long pfn, enum km_type type)

{

arch/frv/include/asm/highmem.h

+1 −1
Original line number Diff line number Diff line
@@ -152,7 +152,7 @@ do { \ 
	asm volatile("tlbpr %0,gr0,#4,#1" : : "r"(vaddr) : "memory");	\

} while(0)



static inline void kunmap_atomic(void *kvaddr, enum km_type type)

static inline void kunmap_atomic_notypecheck(void *kvaddr, enum km_type type)

{

	switch (type) {

        case 0:		__kunmap_atomic_primary(0, 2);	break;

arch/mips/include/asm/highmem.h

+2 −2
Original line number Diff line number Diff line
@@ -48,14 +48,14 @@ extern void kunmap_high(struct page *page); 
extern void *__kmap(struct page *page);

extern void __kunmap(struct page *page);

extern void *__kmap_atomic(struct page *page, enum km_type type);

extern void __kunmap_atomic(void *kvaddr, enum km_type type);

extern void __kunmap_atomic_notypecheck(void *kvaddr, enum km_type type);

extern void *kmap_atomic_pfn(unsigned long pfn, enum km_type type);

extern struct page *__kmap_atomic_to_page(void *ptr);



#define kmap			__kmap

#define kunmap			__kunmap

#define kmap_atomic		__kmap_atomic

#define kunmap_atomic		__kunmap_atomic

#define kunmap_atomic_notypecheck		__kunmap_atomic_notypecheck

#define kmap_atomic_to_page	__kmap_atomic_to_page



#define flush_cache_kmaps()	flush_cache_all()

arch/mips/mm/highmem.c

+2 −2
Original line number Diff line number Diff line
@@ -64,7 +64,7 @@ void *__kmap_atomic(struct page *page, enum km_type type) 
}

EXPORT_SYMBOL(__kmap_atomic);



void __kunmap_atomic(void *kvaddr, enum km_type type)

void __kunmap_atomic_notypecheck(void *kvaddr, enum km_type type)

{

#ifdef CONFIG_DEBUG_HIGHMEM

	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
@@ -87,7 +87,7 @@ void __kunmap_atomic(void *kvaddr, enum km_type type) 


	pagefault_enable();

}

EXPORT_SYMBOL(__kunmap_atomic);

EXPORT_SYMBOL(__kunmap_atomic_notypecheck);



/*

 * This is the same as kmap_atomic() but can map memory that doesn't