[ARM] Fix ARM __raw_read_trylock() implementation

Matthew Wilcox pointed out that the generic implementation
of this is unfit for use.  Here's an ARM optimised version
instead.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 15 insertions, 1 deletions

diff --git a/include/asm-arm/spinlock.h b/include/asm-arm/spinlock.h
index 406ca97a8ab2..e2f1d75171df 100644
--- a/include/asm-arm/spinlock.h
+++ b/include/asm-arm/spinlock.h
@@ -199,7 +199,21 @@ static inline void __raw_read_unlock(raw_rwlock_t *rw)
         : "cc");
 }
 
-#define __raw_read_trylock(lock) generic__raw_read_trylock(lock)
+static inline int __raw_read_trylock(raw_rwlock_t *rw)
+{
+        unsigned long tmp tmp2 = 1;
+
+        __asm__ __volatile__(
+"1:     ldrex   %0, [%2]\n"
+"       adds    %0, %0, #1\n"
+"       strexpl %1, %0, [%2]\n"
+        : "=&r" (tmp), "+r" (tmp2)
+        : "r" (&rw->lock)
+        : "cc");
+
+        smp_mb();
+        return tmp2 == 0;
+}
 
 /* read_can_lock - would read_trylock() succeed? */
 #define __raw_read_can_lock(x)          ((x)->lock < 0x80000000)