ia64: fix sparse warnings with cmpxchg() & xchg()

On IA64, new sparse's warnings where issued after fixing some __rcu
annotations in kernel/bpf/.

These new warnings are false positives and appear on IA64 because on this
architecture, the macros for cmpxchg() and xchg() make casts that ignore
sparse annotations.

This patch contains the minimal patch to fix this issue: adding a missing
cast and some missing '__force'.

Link: https://lore.kernel.org/r/20220601120013.bq5a3ynbkc3hngm5@mail
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Luc Van Oostenryck <[email protected]>
Reported-by: kernel test robot <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Acked-by: Toke Høiland-Jørgensen <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

arch/ia64/include/uapi/asm/cmpxchg.h

@@ -33,24 +33,24 @@ extern void ia64_xchg_called_with_bad_pointer(void);
 									\
 	switch (size) {							\
 	case 1:								\
-		__xchg_result = ia64_xchg1((__u8 *)ptr, x);		\
+		__xchg_result = ia64_xchg1((__u8 __force *)ptr, x);	\
 		break;							\
 									\
 	case 2:								\
-		__xchg_result = ia64_xchg2((__u16 *)ptr, x);		\
+		__xchg_result = ia64_xchg2((__u16 __force *)ptr, x);	\
 		break;							\
 									\
 	case 4:								\
-		__xchg_result = ia64_xchg4((__u32 *)ptr, x);		\
+		__xchg_result = ia64_xchg4((__u32 __force *)ptr, x);	\
 		break;							\
 									\
 	case 8:								\
-		__xchg_result = ia64_xchg8((__u64 *)ptr, x);		\
+		__xchg_result = ia64_xchg8((__u64 __force *)ptr, x);	\
 		break;							\
 	default:							\
 		ia64_xchg_called_with_bad_pointer();			\
 	}								\
-	__xchg_result;							\
+	(__typeof__ (*(ptr)) __force) __xchg_result;			\
 })
 
 #ifndef __KERNEL__
@@ -76,42 +76,42 @@ extern long ia64_cmpxchg_called_with_bad_pointer(void);
 									\
 	switch (size) {							\
 	case 1:								\
-		_o_ = (__u8) (long) (old);				\
+		_o_ = (__u8) (long __force) (old);			\
 		break;							\
 	case 2:								\
-		_o_ = (__u16) (long) (old);				\
+		_o_ = (__u16) (long __force) (old);			\
 		break;							\
 	case 4:								\
-		_o_ = (__u32) (long) (old);				\
+		_o_ = (__u32) (long __force) (old);			\
 		break;							\
 	case 8:								\
-		_o_ = (__u64) (long) (old);				\
+		_o_ = (__u64) (long __force) (old);			\
 		break;							\
 	default:							\
 		break;							\
 	}								\
 	switch (size) {							\
 	case 1:								\
-		_r_ = ia64_cmpxchg1_##sem((__u8 *) ptr, new, _o_);	\
+		_r_ = ia64_cmpxchg1_##sem((__u8 __force *) ptr, new, _o_);	\
 		break;							\
 									\
 	case 2:								\
-		_r_ = ia64_cmpxchg2_##sem((__u16 *) ptr, new, _o_);	\
+		_r_ = ia64_cmpxchg2_##sem((__u16 __force *) ptr, new, _o_);	\
 		break;							\
 									\
 	case 4:								\
-		_r_ = ia64_cmpxchg4_##sem((__u32 *) ptr, new, _o_);	\
+		_r_ = ia64_cmpxchg4_##sem((__u32 __force *) ptr, new, _o_);	\
 		break;							\
 									\
 	case 8:								\
-		_r_ = ia64_cmpxchg8_##sem((__u64 *) ptr, new, _o_);	\
+		_r_ = ia64_cmpxchg8_##sem((__u64 __force *) ptr, new, _o_);	\
 		break;							\
 									\
 	default:							\
 		_r_ = ia64_cmpxchg_called_with_bad_pointer();		\
 		break;							\
 	}								\
-	(__typeof__(old)) _r_;						\
+	(__typeof__(old) __force) _r_;					\
 })
 
 #define cmpxchg_acq(ptr, o, n)	\