bitops: protect variables in bit_clear_unless() macro

mainline inclusion
from mainline-4.20-rc1
commit edfa87281f4fa1b78a21f6db999935a2faa2f6b8
category: bugfix
bugzilla: 5544
CVE: NA

---------------------------

Unprotected naming of local variables within bit_clear_unless() can easily
lead to using the wrong scope.

Noticed this by code review after having hit this issue in set_mask_bits()
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Fixes: 85ad1d13 ("md: set MD_CHANGE_PENDING in a atomic region")
Cc: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Reviewed-by: Nzhengbin <zhengbin13@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/linux/bitops.h

@@ -251,18 +251,18 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
 #endif
 
 #ifndef bit_clear_unless
-#define bit_clear_unless(ptr, _clear, _test)	\
+#define bit_clear_unless(ptr, clear, test)	\
 ({								\
-	const typeof(*ptr) clear = (_clear), test = (_test);	\
-	typeof(*ptr) old, new;					\
+	const typeof(*(ptr)) clear__ = (clear), test__ = (test);\
+	typeof(*(ptr)) old__, new__;				\
 								\
 	do {							\
-		old = READ_ONCE(*ptr);			\
-		new = old & ~clear;				\
-	} while (!(old & test) &&				\
-		 cmpxchg(ptr, old, new) != old);		\
+		old__ = READ_ONCE(*(ptr));			\
+		new__ = old__ & ~clear__;			\
+	} while (!(old__ & test__) &&				\
+		 cmpxchg(ptr, old__, new__) != old__);		\
 								\
-	!(old & test);						\
+	!(old__ & test__);					\
 })
 #endif