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 <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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

14 files changed, 28 insertions, 20 deletions

diff --git a/arch/arm/include/asm/highmem.h b/arch/arm/include/asm/highmem.h
index feb988a7ec37..5aff58126602 100644
--- a/arch/arm/include/asm/highmem.h
+++ b/arch/arm/include/asm/highmem.h
@@ -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
diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index 6ab244062b4a..1fbdb55bfd1b 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -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)
 {
diff --git a/arch/frv/include/asm/highmem.h b/arch/frv/include/asm/highmem.h
index 68e4677fb9e7..cb4c317eaecc 100644
--- a/arch/frv/include/asm/highmem.h
+++ b/arch/frv/include/asm/highmem.h
@@ -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;
diff --git a/arch/mips/include/asm/highmem.h b/arch/mips/include/asm/highmem.h
index 25adfb02923d..75753ca73bfd 100644
--- a/arch/mips/include/asm/highmem.h
+++ b/arch/mips/include/asm/highmem.h
@@ -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()
diff --git a/arch/mips/mm/highmem.c b/arch/mips/mm/highmem.c
index 127d732474bf..6a2b1bf9ef11 100644
--- a/arch/mips/mm/highmem.c
+++ b/arch/mips/mm/highmem.c
@@ -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
diff --git a/arch/mn10300/include/asm/highmem.h b/arch/mn10300/include/asm/highmem.h
index 90f2abb04bfd..b0b187a29b88 100644
--- a/arch/mn10300/include/asm/highmem.h
+++ b/arch/mn10300/include/asm/highmem.h
@@ -91,7 +91,7 @@ static inline unsigned long kmap_atomic(struct page *page, enum km_type type)
         return vaddr;
 }
 
-static inline void kunmap_atomic(unsigned long vaddr, enum km_type type)
+static inline void kunmap_atomic_notypecheck(unsigned long vaddr, enum km_type type)
 {
 #if HIGHMEM_DEBUG
         enum fixed_addresses idx = type + KM_TYPE_NR * smp_processor_id();
diff --git a/arch/parisc/include/asm/cacheflush.h b/arch/parisc/include/asm/cacheflush.h
index 4556d820128a..dba11aedce1b 100644
--- a/arch/parisc/include/asm/cacheflush.h
+++ b/arch/parisc/include/asm/cacheflush.h
@@ -132,7 +132,7 @@ static inline void *kmap_atomic(struct page *page, enum km_type idx)
         return page_address(page);
 }
 
-static inline void kunmap_atomic(void *addr, enum km_type idx)
+static inline void kunmap_atomic_notypecheck(void *addr, enum km_type idx)
 {
         kunmap_parisc(addr);
         pagefault_enable();
diff --git a/arch/powerpc/include/asm/highmem.h b/arch/powerpc/include/asm/highmem.h
index a74c4ee6c020..d10d64a4be38 100644
--- a/arch/powerpc/include/asm/highmem.h
+++ b/arch/powerpc/include/asm/highmem.h
@@ -62,7 +62,7 @@ extern void *kmap_high(struct page *page);
 extern void kunmap_high(struct page *page);
 extern void *kmap_atomic_prot(struct page *page, enum km_type type,
                               pgprot_t prot);
-extern void kunmap_atomic(void *kvaddr, enum km_type type);
+extern void kunmap_atomic_notypecheck(void *kvaddr, enum km_type type);
 
 static inline void *kmap(struct page *page)
 {
diff --git a/arch/powerpc/mm/highmem.c b/arch/powerpc/mm/highmem.c
index c2186c74c85a..857d4173f9c6 100644
--- a/arch/powerpc/mm/highmem.c
+++ b/arch/powerpc/mm/highmem.c
@@ -52,7 +52,7 @@ void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot)
 }
 EXPORT_SYMBOL(kmap_atomic_prot);
 
-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;
@@ -74,4 +74,4 @@ void kunmap_atomic(void *kvaddr, enum km_type type)
 #endif
         pagefault_enable();
 }
-EXPORT_SYMBOL(kunmap_atomic);
+EXPORT_SYMBOL(kunmap_atomic_notypecheck);
diff --git a/arch/sparc/include/asm/highmem.h b/arch/sparc/include/asm/highmem.h
index 3de42e776274..ec23b0a87b98 100644
--- a/arch/sparc/include/asm/highmem.h
+++ b/arch/sparc/include/asm/highmem.h
@@ -71,7 +71,7 @@ static inline 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 struct page *kmap_atomic_to_page(void *vaddr);
 
 #define flush_cache_kmaps()     flush_cache_all()
diff --git a/arch/sparc/mm/highmem.c b/arch/sparc/mm/highmem.c
index 7916feba6e4a..e139e9cbf5f7 100644
--- a/arch/sparc/mm/highmem.c
+++ b/arch/sparc/mm/highmem.c
@@ -65,7 +65,7 @@ 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;
@@ -100,7 +100,7 @@ void kunmap_atomic(void *kvaddr, enum km_type type)
 
         pagefault_enable();
 }
-EXPORT_SYMBOL(kunmap_atomic);
+EXPORT_SYMBOL(kunmap_atomic_notypecheck);
 
 /* We may be fed a pagetable here by ptep_to_xxx and others. */
 struct page *kmap_atomic_to_page(void *ptr)
diff --git a/arch/x86/include/asm/highmem.h b/arch/x86/include/asm/highmem.h
index a726650fc80f..8caac76ac324 100644
--- a/arch/x86/include/asm/highmem.h
+++ b/arch/x86/include/asm/highmem.h
@@ -61,7 +61,7 @@ void *kmap(struct page *page);
 void kunmap(struct page *page);
 void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot);
 void *kmap_atomic(struct page *page, enum km_type type);
-void kunmap_atomic(void *kvaddr, enum km_type type);
+void kunmap_atomic_notypecheck(void *kvaddr, enum km_type type);
 void *kmap_atomic_pfn(unsigned long pfn, enum km_type type);
 void *kmap_atomic_prot_pfn(unsigned long pfn, enum km_type type, pgprot_t prot);
 struct page *kmap_atomic_to_page(void *ptr);
diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
index 63a6ba66cbe0..5e8fa12ef861 100644
--- a/arch/x86/mm/highmem_32.c
+++ b/arch/x86/mm/highmem_32.c
@@ -53,7 +53,7 @@ void *kmap_atomic(struct page *page, enum km_type type)
         return kmap_atomic_prot(page, type, kmap_prot);
 }
 
-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;
         enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();
@@ -102,7 +102,7 @@ struct page *kmap_atomic_to_page(void *ptr)
 EXPORT_SYMBOL(kmap);
 EXPORT_SYMBOL(kunmap);
 EXPORT_SYMBOL(kmap_atomic);
-EXPORT_SYMBOL(kunmap_atomic);
+EXPORT_SYMBOL(kunmap_atomic_notypecheck);
 EXPORT_SYMBOL(kmap_atomic_prot);
 EXPORT_SYMBOL(kmap_atomic_to_page);
 
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 <linux/fs.h>
+#include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 
@@ -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)