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From: Cesar Eduardo Barros on 28 May 2010 07:00
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 pointer passed to it is convertible to a
struct page * but it is not a void * (verified by trying to convert it
to a pointer to a dummy struct).

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).

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 *?

Cc: Russell King <linux(a)arm.linux.org.uk> (arch/arm)
Cc: Ralf Baechle <ralf(a)linux-mips.org> (arch/mips)
Cc: David Howells <dhowells(a)redhat.com> (arch/frv, arch/mn10300)
Cc: Koichi Yasutake <yasutake.koichi(a)jp.panasonic.com> (arch/mn10300)
Cc: Benjamin Herrenschmidt <benh(a)kernel.crashing.org> (arch/powerpc)
Cc: Paul Mackerras <paulus(a)samba.org> (arch/powerpc)
Cc: "David S. Miller" <davem(a)davemloft.net> (arch/sparc)
Cc: Thomas Gleixner <tglx(a)linutronix.de> (arch/x86)
Cc: Ingo Molnar <mingo(a)redhat.com> (arch/x86)
Cc: "H. Peter Anvin" <hpa(a)zytor.com> (arch/x86)
Cc: x86(a)kernel.org (arch/x86)
Cc: Arnd Bergmann <arnd(a)arndb.de> (include/asm-generic)
Cc: Rusty Russell <rusty(a)rustcorp.com.au> ("Hard To Misuse" list)
Signed-off-by: Cesar Eduardo Barros <cesarb(a)cesarb.net>
---
arch/arm/include/asm/highmem.h | 2 +-
arch/arm/mm/highmem.c | 4 ++--
arch/frv/include/asm/highmem.h | 2 +-
arch/mips/include/asm/highmem.h | 4 ++--
arch/mips/mm/highmem.c | 4 ++--
arch/mn10300/include/asm/highmem.h | 2 +-
arch/powerpc/include/asm/highmem.h | 2 +-
arch/powerpc/mm/highmem.c | 4 ++--
arch/sparc/include/asm/highmem.h | 2 +-
arch/sparc/mm/highmem.c | 4 ++--
arch/x86/include/asm/highmem.h | 2 +-
arch/x86/mm/highmem_32.c | 4 ++--
include/linux/highmem.h | 12 +++++++++++-
13 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/arch/arm/include/asm/highmem.h b/arch/arm/include/asm/highmem.h
index feb988a..5aff581 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 77b030f..128c2aa 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -73,7 +73,7 @@ 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();
@@ -94,7 +94,7 @@ 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 68e4677..cb4c317 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 25adfb0..75753ca 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 127d732..6a2b1bf 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 90f2abb..b0b187a 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/powerpc/include/asm/highmem.h b/arch/powerpc/include/asm/highmem.h
index a74c4ee..d10d64a 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 c2186c7..857d417 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 3de42e7..ec23b0a 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 7916feb..e139e9c 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 a726650..8caac76 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 63a6ba6..5e8fa12 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 caafd05..9dc728c 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 +82,15 @@ 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() */
+struct __kunmap_atomic_dummy {};
+#define kunmap_atomic(addr, idx) do { \
+ BUILD_BUG_ON( \
+ __builtin_types_compatible_p(typeof(addr), struct page *) && \
+ !__builtin_types_compatible_p(typeof(addr), struct __kunmap_atomic_dummy *)); \
+ 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)
--
1.6.6.1

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