[PATCH v2 0/2] percpu: Add a test case and fix for clang

[PATCH v2 0/2] percpu: Add a test case and fix for clang

[Andy Shevchenko]

Add a test case to percpu to check a corner case with the specific
64-bit unsigned value. This test case shows why the first patch is
done in the way it's done.

The before and after has been tested with binary comparison of
the percpu_test module and runnig it on the real Intel system.

v2:
- updated Subject (Dave)
- added test case

Andy Shevchenko (2):
  x86/percpu: Fix clang warning when dealing with unsigned types
  percpu: Add a test case for the specific 64-bit value addition

 arch/x86/include/asm/percpu.h |  7 ++++---
 lib/percpu_test.c             | 11 ++++++++++-
 2 files changed, 14 insertions(+), 4 deletions(-)

-- 
2.43.0.rc1.1336.g36b5255a03ac

[PATCH v2 1/2] x86/percpu: Fix clang warning when dealing with unsigned types

[Andy Shevchenko]

When percpu_add_op() is used with an 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@linux.intel.com>
---
 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

[PATCH v2 2/2] percpu: Add a test case for the specific 64-bit value addition

[Andy Shevchenko]

It might be a corner case when we add UINT_MAX as 64-bit unsigned value
to the percpu variable as it's not the same as -1 (ULONG_LONG_MAX).
Add a test case for that.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 lib/percpu_test.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/lib/percpu_test.c b/lib/percpu_test.c
index 4a3d70bbc1a0..ce7124b16dab 100644
--- a/lib/percpu_test.c
+++ b/lib/percpu_test.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-only
+#include <linux/limits.h>
 #include <linux/module.h>
 
 /* validate @native and @pcp counter values match @expected */
@@ -24,8 +25,9 @@ static int __init percpu_test_init(void)
 	 * +ul_one/-ul_one below would replace with inc/dec instructions.
 	 */
 	volatile unsigned int ui_one = 1;
-	long l = 0;
+	unsigned long long ull = 0;
 	unsigned long ul = 0;
+	long l = 0;
 
 	pr_info("percpu test start\n");
 
@@ -112,6 +114,13 @@ static int __init percpu_test_init(void)
 	CHECK(ul, ulong_counter, -1);
 	CHECK(ul, ulong_counter, ULONG_MAX);
 
+	ul = ull = 0;
+	__this_cpu_write(ulong_counter, 0);
+
+	ul = ull += UINT_MAX;
+	__this_cpu_add(ulong_counter, ull);
+	CHECK(ul, ulong_counter, UINT_MAX);
+
 	ul = 3;
 	__this_cpu_write(ulong_counter, 3);
 
-- 
2.43.0.rc1.1336.g36b5255a03ac