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

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

[Naresh Kamboju]

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.


## Source
* Git tree: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
* Git sha: 596aae841edf981aab1df1845e6df012bed94594
* Git describe: v6.12.39-159-g596aae841edf
* Architectures: arm64 x86
* Toolchains: Debian clang version 22.0.0
(++20250721112855+43a829a7e894-1~exp1~20250721112913.1588)
* Kconfigs: allyesconfig

## Build
* Build log: https://regressions.linaro.org/lkft/linux-stable-rc-linux-6.12.y/v6.12.39-159-g596aae841edf/build/clang-nightly-allyesconfig/
* Build run: https://regressions.linaro.org/lkft/linux-stable-rc-linux-6.12.y/v6.12.39-159-g596aae841edf/testruns/1703644/
* Build link: https://storage.tuxsuite.com/public/linaro/lkft/builds/30EXE6Cnct6e7DCgsWWrXlMdO0z/
* Kernel config:
https://storage.tuxsuite.com/public/linaro/lkft/builds/30EXE6Cnct6e7DCgsWWrXlMdO0z/config

## Steps to reproduce
* tuxmake --runtime podman --target-arch arm64 --toolchain
clang-nightly --kconfig allyesconfig LLVM=1 LLVM_IAS=1

--
Linaro LKFT
https://lkft.linaro.org

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

[Marco Elver]

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