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authorCatalin Marinas <catalin.marinas@arm.com>2009-09-18 23:27:05 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2009-09-18 23:30:11 +0100
commit200b812d0084f800bc52465e273b118ff5f8141f (patch)
tree6dbef78960ad7b83a76df064751275913583068c /arch/arm/include
parentdf58bee21ed218cb7dfb561a590b1bd2a99531cf (diff)
Clear the exclusive monitor when returning from an exception
The patch adds a CLREX or dummy STREX to the exception return path. This is needed because several atomic/locking operations use a pair of LDREX/STREXEQ and the EQ condition may not always be satisfied. This would leave the exclusive monitor status set and may cause problems with atomic/locking operations in the interrupted code. With this patch, the atomic_set() operation can be a simple STR instruction (on SMP systems, the global exclusive monitor is cleared by STR anyway). Clearing the exclusive monitor during context switch is no longer needed as this is handled by the exception return path anyway. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Reported-by: Jamie Lokier <jamie@shareable.org>
Diffstat (limited to 'arch/arm/include')
-rw-r--r--arch/arm/include/asm/atomic.h26
1 files changed, 7 insertions, 19 deletions
diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h
index 9ed2377fe8e5..d0daeab2234e 100644
--- a/arch/arm/include/asm/atomic.h
+++ b/arch/arm/include/asm/atomic.h
@@ -19,31 +19,21 @@
#ifdef __KERNEL__
+/*
+ * On ARM, ordinary assignment (str instruction) doesn't clear the local
+ * strex/ldrex monitor on some implementations. The reason we can use it for
+ * atomic_set() is the clrex or dummy strex done on every exception return.
+ */
#define atomic_read(v) ((v)->counter)
+#define atomic_set(v,i) (((v)->counter) = (i))
#if __LINUX_ARM_ARCH__ >= 6
/*
* ARMv6 UP and SMP safe atomic ops. We use load exclusive and
* store exclusive to ensure that these are atomic. We may loop
- * to ensure that the update happens. Writing to 'v->counter'
- * without using the following operations WILL break the atomic
- * nature of these ops.
+ * to ensure that the update happens.
*/
-static inline void atomic_set(atomic_t *v, int i)
-{
- unsigned long tmp;
-
- __asm__ __volatile__("@ atomic_set\n"
-"1: ldrex %0, [%1]\n"
-" strex %0, %2, [%1]\n"
-" teq %0, #0\n"
-" bne 1b"
- : "=&r" (tmp)
- : "r" (&v->counter), "r" (i)
- : "cc");
-}
-
static inline void atomic_add(int i, atomic_t *v)
{
unsigned long tmp;
@@ -163,8 +153,6 @@ static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)
#error SMP not supported on pre-ARMv6 CPUs
#endif
-#define atomic_set(v,i) (((v)->counter) = (i))
-
static inline int atomic_add_return(int i, atomic_t *v)
{
unsigned long flags;