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Date: Tue, 26 May 2009 15:59:50 +0100
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc: Jamie Lokier <jamie@...reable.org>,
Catalin Marinas <catalin.marinas@....com>,
linux-arm-kernel@...ts.arm.linux.org.uk,
linux-kernel@...r.kernel.org
Subject: Re: Broken ARM atomic ops wrt memory barriers (was : [PATCH] Add
cmpxchg support for ARMv6+ systems)
Here's an updated version of the patch:
adds a data memory barrier before and after these operations:
- test_and_xxx_bit()
- atomic_xxx_return()
- atomic_cmpxchg()
- __xchg
Also:
- converts smp_mb__*_atomic_*() to use smp_mb()
- ensures __kuser_memory_barrier uses the right instruction on ARMv7
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 6116e48..15f8a09 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -114,3 +114,16 @@
.align 3; \
.long 9999b,9001f; \
.previous
+
+/*
+ * SMP data memory barrier
+ */
+ .macro smp_dmb
+#ifdef CONFIG_SMP
+#if __LINUX_ARM_ARCH__ >= 7
+ dmb
+#elif __LINUX_ARM_ARCH__ == 6
+ mcr p15, 0, r0, c7, c10, 5 @ dmb
+#endif
+#endif
+ .endm
diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h
index ee99723..16b52f3 100644
--- a/arch/arm/include/asm/atomic.h
+++ b/arch/arm/include/asm/atomic.h
@@ -44,11 +44,29 @@ static inline void atomic_set(atomic_t *v, int i)
: "cc");
}
+static inline void atomic_add(int i, atomic_t *v)
+{
+ unsigned long tmp;
+ int result;
+
+ __asm__ __volatile__("@ atomic_add\n"
+"1: ldrex %0, [%2]\n"
+" add %0, %0, %3\n"
+" strex %1, %0, [%2]\n"
+" teq %1, #0\n"
+" bne 1b"
+ : "=&r" (result), "=&r" (tmp)
+ : "r" (&v->counter), "Ir" (i)
+ : "cc");
+}
+
static inline int atomic_add_return(int i, atomic_t *v)
{
unsigned long tmp;
int result;
+ smp_mb();
+
__asm__ __volatile__("@ atomic_add_return\n"
"1: ldrex %0, [%2]\n"
" add %0, %0, %3\n"
@@ -59,14 +77,34 @@ static inline int atomic_add_return(int i, atomic_t *v)
: "r" (&v->counter), "Ir" (i)
: "cc");
+ smp_mb();
+
return result;
}
+static inline void atomic_sub(int i, atomic_t *v)
+{
+ unsigned long tmp;
+ int result;
+
+ __asm__ __volatile__("@ atomic_sub\n"
+"1: ldrex %0, [%2]\n"
+" sub %0, %0, %3\n"
+" strex %1, %0, [%2]\n"
+" teq %1, #0\n"
+" bne 1b"
+ : "=&r" (result), "=&r" (tmp)
+ : "r" (&v->counter), "Ir" (i)
+ : "cc");
+}
+
static inline int atomic_sub_return(int i, atomic_t *v)
{
unsigned long tmp;
int result;
+ smp_mb();
+
__asm__ __volatile__("@ atomic_sub_return\n"
"1: ldrex %0, [%2]\n"
" sub %0, %0, %3\n"
@@ -77,6 +115,8 @@ static inline int atomic_sub_return(int i, atomic_t *v)
: "r" (&v->counter), "Ir" (i)
: "cc");
+ smp_mb();
+
return result;
}
@@ -84,6 +124,8 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
{
unsigned long oldval, res;
+ smp_mb();
+
do {
__asm__ __volatile__("@ atomic_cmpxchg\n"
"ldrex %1, [%2]\n"
@@ -95,6 +137,8 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
: "cc");
} while (res);
+ smp_mb();
+
return oldval;
}
@@ -135,6 +179,7 @@ static inline int atomic_add_return(int i, atomic_t *v)
return val;
}
+#define atomic_add(i, v) (void) atomic_add_return(i, v)
static inline int atomic_sub_return(int i, atomic_t *v)
{
@@ -148,6 +193,7 @@ static inline int atomic_sub_return(int i, atomic_t *v)
return val;
}
+#define atomic_sub(i, v) (void) atomic_sub_return(i, v)
static inline int atomic_cmpxchg(atomic_t *v, int old, int new)
{
@@ -187,10 +233,8 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
}
#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
-#define atomic_add(i, v) (void) atomic_add_return(i, v)
-#define atomic_inc(v) (void) atomic_add_return(1, v)
-#define atomic_sub(i, v) (void) atomic_sub_return(i, v)
-#define atomic_dec(v) (void) atomic_sub_return(1, v)
+#define atomic_inc(v) atomic_add(1, v)
+#define atomic_dec(v) atomic_sub(1, v)
#define atomic_inc_and_test(v) (atomic_add_return(1, v) == 0)
#define atomic_dec_and_test(v) (atomic_sub_return(1, v) == 0)
@@ -200,11 +244,10 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
#define atomic_add_negative(i,v) (atomic_add_return(i, v) < 0)
-/* Atomic operations are already serializing on ARM */
-#define smp_mb__before_atomic_dec() barrier()
-#define smp_mb__after_atomic_dec() barrier()
-#define smp_mb__before_atomic_inc() barrier()
-#define smp_mb__after_atomic_inc() barrier()
+#define smp_mb__before_atomic_dec() smp_mb()
+#define smp_mb__after_atomic_dec() smp_mb()
+#define smp_mb__before_atomic_inc() smp_mb()
+#define smp_mb__after_atomic_inc() smp_mb()
#include <asm-generic/atomic.h>
#endif
diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
index bd4dc8e..e9889c2 100644
--- a/arch/arm/include/asm/system.h
+++ b/arch/arm/include/asm/system.h
@@ -248,6 +248,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
unsigned int tmp;
#endif
+ smp_mb();
+
switch (size) {
#if __LINUX_ARM_ARCH__ >= 6
case 1:
@@ -258,7 +260,7 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
" bne 1b"
: "=&r" (ret), "=&r" (tmp)
: "r" (x), "r" (ptr)
- : "memory", "cc");
+ : "cc");
break;
case 4:
asm volatile("@ __xchg4\n"
@@ -268,7 +270,7 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
" bne 1b"
: "=&r" (ret), "=&r" (tmp)
: "r" (x), "r" (ptr)
- : "memory", "cc");
+ : "cc");
break;
#elif defined(swp_is_buggy)
#ifdef CONFIG_SMP
@@ -293,20 +295,21 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
" swpb %0, %1, [%2]"
: "=&r" (ret)
: "r" (x), "r" (ptr)
- : "memory", "cc");
+ : "cc");
break;
case 4:
asm volatile("@ __xchg4\n"
" swp %0, %1, [%2]"
: "=&r" (ret)
: "r" (x), "r" (ptr)
- : "memory", "cc");
+ : "cc");
break;
#endif
default:
__bad_xchg(ptr, size), ret = 0;
break;
}
+ smp_mb();
return ret;
}
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index d662a2f..83b1da6 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -815,10 +815,7 @@ __kuser_helper_start:
*/
__kuser_memory_barrier: @ 0xffff0fa0
-
-#if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_SMP)
- mcr p15, 0, r0, c7, c10, 5 @ dmb
-#endif
+ smp_dmb
usr_ret lr
.align 5
diff --git a/arch/arm/lib/bitops.h b/arch/arm/lib/bitops.h
index 2e787d4..c7f2627 100644
--- a/arch/arm/lib/bitops.h
+++ b/arch/arm/lib/bitops.h
@@ -18,12 +18,14 @@
mov r2, #1
add r1, r1, r0, lsr #3 @ Get byte offset
mov r3, r2, lsl r3 @ create mask
+ smp_dmb
1: ldrexb r2, [r1]
ands r0, r2, r3 @ save old value of bit
\instr r2, r2, r3 @ toggle bit
strexb ip, r2, [r1]
cmp ip, #0
bne 1b
+ smp_dmb
cmp r0, #0
movne r0, #1
2: mov pc, lr
--
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