Re: [PATCH 6.12 000/158] 6.12.40-rc1 review

[Marco Elver <elver@google.com>]

On Tue, Jul 22, 2025 at 11:30PM +0530, Naresh Kamboju wrote:
> On Tue, 22 Jul 2025 at 19:27, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > This is the start of the stable review cycle for the 6.12.40 release.
> > There are 158 patches in this series, all will be posted as a response
> > to this one.  If anyone has any issues with these being applied, please
> > let me know.
> >
> > Responses should be made by Thu, 24 Jul 2025 13:43:10 +0000.
> > Anything received after that time might be too late.
> >
> > The whole patch series can be found in one patch at:
> >         https://www.kernel.org/pub/linux/kernel/v6.x/stable-review/patch-6.12.40-rc1.gz
> > or in the git tree and branch at:
> >         git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-6.12.y
> > and the diffstat can be found below.
> >
> > thanks,
> >
> > greg k-h
> 
> With addition to the previous report on the stable-rc 6.15.8-rc1 review
> While building allyesconfig build for arm64 and x86 with the toolchain
> clang-nightly version 22.0.0 the following build warnings / errors
> noticed on the stable-rc 6.12.40-rc1 review.
> 
> Regression Analysis:
> - New regression? Yes
> - Reproducibility? Yes
> 
> Build regression: arm64 x86 kcsan_test.c error variable 'dummy' is
> uninitialized when passed as a const pointer argument here
> 
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> 
> ## Build log
> 
> kernel/kcsan/kcsan_test.c:591:41: error: variable 'dummy' is
> uninitialized when passed as a const pointer argument here
> [-Werror,-Wuninitialized-const-pointer]
>   591 |         KCSAN_EXPECT_READ_BARRIER(atomic_read(&dummy), false);
>       |                                                ^~~~~
> 1 error generated.

Thanks for catching this. Newer versions of Clang seem to be getting
smarter. We can silence the warning with the below patch:

From 56c920457a4e7077b83aafb0c9c8105fb98b0158 Mon Sep 17 00:00:00 2001
From: Marco Elver <elver@google.com>
Date: Tue, 22 Jul 2025 20:19:17 +0200
Subject: [PATCH] kcsan/test: Initialize dummy variable

Newer compiler versions rightfully point out:

 kernel/kcsan/kcsan_test.c:591:41: error: variable 'dummy' is
 uninitialized when passed as a const pointer argument here
 [-Werror,-Wuninitialized-const-pointer]
   591 |         KCSAN_EXPECT_READ_BARRIER(atomic_read(&dummy), false);
       |                                                ^~~~~
 1 error generated.

Although this particular test does not care about the value stored in
the dummy atomic variable, let's silence the warning.

Link: https://lkml.kernel.org/r/CA+G9fYu8JY=k-r0hnBRSkQQrFJ1Bz+ShdXNwC1TNeMt0eXaxeA@mail.gmail.com
Fixes: 8bc32b348178 ("kcsan: test: Add test cases for memory barrier instrumentation")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Marco Elver <elver@google.com>
---
 kernel/kcsan/kcsan_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
index c2871180edcc..49ab81faaed9 100644
--- a/kernel/kcsan/kcsan_test.c
+++ b/kernel/kcsan/kcsan_test.c
@@ -533,7 +533,7 @@ static void test_barrier_nothreads(struct kunit *test)
 	struct kcsan_scoped_access *reorder_access = NULL;
 #endif
 	arch_spinlock_t arch_spinlock = __ARCH_SPIN_LOCK_UNLOCKED;
-	atomic_t dummy;
+	atomic_t dummy = ATOMIC_INIT(0);
 
 	KCSAN_TEST_REQUIRES(test, reorder_access != NULL);
 	KCSAN_TEST_REQUIRES(test, IS_ENABLED(CONFIG_SMP));
-- 
2.50.0.727.gbf7dc18ff4-goog