The patch titled
Subject: x86/percpu: fix clang warning when dealing with unsigned types
has been added to the -mm mm-unstable branch. Its filename is
x86-percpu-fix-clang-warning-when-dealing-with-unsigned-types.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-percpu-fix-clang-warning-when-dealing-with-unsigned-types.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Subject: x86/percpu: fix clang warning when dealing with unsigned types
Date: Wed, 16 Oct 2024 21:23:51 +0300
Patch series "percpu: Add a test case and fix for clang", v2.
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.
This patch (of 2):
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.
Link: https://lkml.kernel.org/r/20241016182635.1156168-1-andriy.shevchenko@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20241016182635.1156168-2-andriy.shevchenko@xxxxxxxxxxxxxxx
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/percpu.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/percpu.h~x86-percpu-fix-clang-warning-when-dealing-with-unsigned-types
+++ a/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__; \
_
Patches currently in -mm which might be from andriy.shevchenko@xxxxxxxxxxxxxxx are
mm-remove-unused-stub-for-can_swapin_thp.patch
x86-percpu-fix-clang-warning-when-dealing-with-unsigned-types.patch
percpu-add-a-test-case-for-the-specific-64-bit-value-addition.patch
resource-replace-open-coded-resource_intersection.patch
resource-introduce-is_type_match-helper-and-use-it.patch
