Re: clang: mm/khugepaged.c:1729:7: error: variable 'index' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Oct 26, 2022 at 01:43:48AM +0530, Naresh Kamboju wrote:
> Following build warning / errors noticed while building x86_64 with clang
> on Linux next-20221025 tag.
> 
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> 
> ## Build
> * kernel: 6.1.0-rc2
> * git: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next
> * git branch: master
> * git commit: 89bf6e28373beef9577fa71f996a5f73a569617c
> * git describe: next-20221025
> * test details:
> https://qa-reports.linaro.org/lkft/linux-next-master-sanity/build/next-20221025
> 
> ## Test Regressions (compared to next-20221024)
> Regressions found on x86_64:
> 
>  - clang-nightly-lkftconfig
>  - clang-12-lkftconfig
>  - clang-14-lkftconfig
>  - clang-13-lkftconfig
>  - clang-14-lkftconfig-kcsan
> 
> make --silent --keep-going --jobs=8
> O=/home/tuxbuild/.cache/tuxmake/builds/1/build LLVM=1 LLVM_IAS=1
> ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- 'HOSTCC=sccache clang'
> 'CC=sccache clang'
> mm/khugepaged.c:1729:7: error: variable 'index' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>                 if (!xas_nomem(&xas, GFP_KERNEL)) {
>                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:2063:47: note: uninitialized use occurs here
>         trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem,
>                                                      ^~~~~
> mm/khugepaged.c:1729:3: note: remove the 'if' if its condition is always false
>                 if (!xas_nomem(&xas, GFP_KERNEL)) {
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:1716:6: error: variable 'index' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (result != SCAN_SUCCEED)
>             ^~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:2063:47: note: uninitialized use occurs here
>         trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem,
>                                                      ^~~~~
> mm/khugepaged.c:1716:2: note: remove the 'if' if its condition is always false
>         if (result != SCAN_SUCCEED)
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:1705:15: note: initialize the variable 'index' to
> silence this warning
>         pgoff_t index, end = start + HPAGE_PMD_NR;
>                      ^
>                       = 0
> mm/khugepaged.c:1729:7: error: variable 'nr' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>                 if (!xas_nomem(&xas, GFP_KERNEL)) {
>                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:2064:15: note: uninitialized use occurs here
>                 addr, file, nr, result);
>                             ^~
> mm/khugepaged.c:1729:3: note: remove the 'if' if its condition is always false
>                 if (!xas_nomem(&xas, GFP_KERNEL)) {
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:1716:6: error: variable 'nr' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (result != SCAN_SUCCEED)
>             ^~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:2064:15: note: uninitialized use occurs here
>                 addr, file, nr, result);
>                             ^~
> mm/khugepaged.c:1716:2: note: remove the 'if' if its condition is always false
>         if (result != SCAN_SUCCEED)
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/khugepaged.c:1710:8: note: initialize the variable 'nr' to silence
> this warning
>         int nr;
>               ^
>                = 0
> 4 errors generated.
> make[3]: *** [scripts/Makefile.build:250: mm/khugepaged.o] Error 1

I sent
https://lore.kernel.org/20221025173407.3423241-1-nathan@kernel.org/ for
this earlier today.

Cheers,
Nathan