[PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add_op()

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

When percpu_add_op() is used with unsigned argument, it prevents kernel builds
with clang, `make W=1` and CONFIG_WERROR=y:

net/ipv4/tcp_output.c:187:3: error: result of comparison of constant -1 with expression of type 'u8' (aka 'unsigned char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
  187 |                 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  188 |                               tp->compressed_ack);
      |                               ~~~~~~~~~~~~~~~~~~~
...
arch/x86/include/asm/percpu.h:238:31: note: expanded from macro 'percpu_add_op'
  238 |                               ((val) == 1 || (val) == -1)) ?            \
      |                                              ~~~~~ ^  ~~

Fix this by casting -1 to the type of the parameter and then compare.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/percpu.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index c55a79d5feae..e525cd85f999 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -234,9 +234,10 @@ do {									\
  */
 #define percpu_add_op(size, qual, var, val)				\
 do {									\
-	const int pao_ID__ = (__builtin_constant_p(val) &&		\
-			      ((val) == 1 || (val) == -1)) ?		\
-				(int)(val) : 0;				\
+	const int pao_ID__ =						\
+		(__builtin_constant_p(val) &&				\
+			((val) == 1 ||					\
+			 (val) == (typeof(val))-1)) ? (int)(val) : 0;	\
 									\
 	if (0) {							\
 		typeof(var) pao_tmp__;					\
-- 
2.43.0.rc1.1336.g36b5255a03ac