From 597781f3e51f48ef8e67be772196d9e9673752c4 Mon Sep 17 00:00:00 2001 From: Cesar Eduardo Barros Date: Mon, 9 Aug 2010 17:18:32 -0700 Subject: 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: Cesar Eduardo Barros Cc: Russell King (arch/arm) Cc: Ralf Baechle (arch/mips) Cc: David Howells (arch/frv, arch/mn10300) Cc: Koichi Yasutake (arch/mn10300) Cc: Kyle McMartin (arch/parisc) Cc: Helge Deller (arch/parisc) Cc: "James E.J. Bottomley" (arch/parisc) Cc: Benjamin Herrenschmidt (arch/powerpc) Cc: Paul Mackerras (arch/powerpc) Cc: "David S. Miller" (arch/sparc) Cc: Thomas Gleixner (arch/x86) Cc: Ingo Molnar (arch/x86) Cc: "H. Peter Anvin" (arch/x86) Cc: Arnd Bergmann (include/asm-generic) Cc: Rusty Russell ("Hard To Misuse" list) Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/highmem.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/highmem.h b/include/linux/highmem.h index caafd0561aa1..67460f010224 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -2,6 +2,7 @@ #define _LINUX_HIGHMEM_H #include +#include #include #include @@ -72,7 +73,7 @@ static inline void *kmap_atomic(struct page *page, enum km_type idx) } #define kmap_atomic_prot(page, idx, prot) kmap_atomic(page, idx) -#define kunmap_atomic(addr, idx) do { pagefault_enable(); } while (0) +#define kunmap_atomic_notypecheck(addr, idx) do { pagefault_enable(); } while (0) #define kmap_atomic_pfn(pfn, idx) kmap_atomic(pfn_to_page(pfn), (idx)) #define kmap_atomic_to_page(ptr) virt_to_page(ptr) @@ -81,6 +82,13 @@ static inline void *kmap_atomic(struct page *page, enum km_type idx) #endif /* CONFIG_HIGHMEM */ +/* Prevent people trying to call kunmap_atomic() as if it were kunmap() */ +/* kunmap_atomic() should get the return value of kmap_atomic, not the page. */ +#define kunmap_atomic(addr, idx) do { \ + BUILD_BUG_ON(__same_type((addr), struct page *)); \ + kunmap_atomic_notypecheck((addr), (idx)); \ + } while (0) + /* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */ #ifndef clear_user_highpage static inline void clear_user_highpage(struct page *page, unsigned long vaddr) -- cgit v1.2.3-59-g8ed1b