linux-kernel - Re: mm/mmap.c:939:11: error: variable 'next' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]

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Date:   Thu, 23 Mar 2023 10:43:21 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev,
        linux-mm <linux-mm@...ck.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: mm/mmap.c:939:11: error: variable 'next' is used uninitialized
 whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]

On 3/23/23 08:58, Naresh Kamboju wrote:
> Following multiple build warnings / errors noticed while building
> Linux next-20230323 with clang-16 for x86_64.
> 
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> 
> Build warnings / errors:
> ---------
> mm/mmap.c:939:11: error: variable 'next' is used uninitialized
> whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>         else if (!curr)
>                  ^~~~~
> mm/mmap.c:952:15: note: uninitialized use occurs here
>         merge_next = next && mpol_equal(policy, vma_policy(next)) &&
>                      ^~~~
> mm/mmap.c:939:7: note: remove the 'if' if its condition is always true
>         else if (!curr)
>              ^~~~~~~~~~
> mm/mmap.c:912:36: note: initialize the variable 'next' to silence this warning
>         struct vm_area_struct *curr, *next, *res;
>                                           ^
>                                            = NULL

Same issue as https://lore.kernel.org/all/CA%2BG9fYvBxp38KEggtvtvVtGMaSBdL3NDV9ns%3DZi9-Jtx7H9g1A@mail.gmail.com/
Thus already resolved in the next -next hopefully.

> 1 error generated.
> make[3]: *** [scripts/Makefile.build:252: mm/mmap.o] Error 1
> 
> mm/vmalloc.c:3543:6: error: variable 'remains' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/vmalloc.c:3587:17: note: uninitialized use occurs here
>         return count - remains + zero_iter(iter, remains);
>                        ^~~~~~~
> mm/vmalloc.c:3543:2: note: remove the 'if' if its condition is always false
>         if (bitmap_empty(vb->used_map, VMAP_BBMAP_BITS)) {
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/vmalloc.c:3539:6: error: variable 'remains' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (!vb)
>             ^~~
> mm/vmalloc.c:3587:17: note: uninitialized use occurs here
>         return count - remains + zero_iter(iter, remains);
>                        ^~~~~~~
> mm/vmalloc.c:3539:2: note: remove the 'if' if its condition is always false
>         if (!vb)
>         ^~~~~~~~
> mm/vmalloc.c:3524:16: note: initialize the variable 'remains' to
> silence this warning
>         size_t remains, n;
>                       ^
>                        = 0
> 2 errors generated.
> make[3]: *** [scripts/Makefile.build:252: mm/vmalloc.o] Error 1
> make[3]: Target 'mm/' not remade because of errors.
> 
> steps to reproduce:
> ----------
> 
> tuxmake  \
>   --runtime podman \
>   --target-arch x86_64 \
>   --toolchain clang-16 LLVM=1 LLVM_IAS=1 \
>   --kconfig https://storage.tuxsuite.com/public/linaro/lkft/builds/2NOjxURhByyb4dR3Ld788iuYvAR/config
> 
> Related discussion on mailing list,
>  - https://lore.kernel.org/llvm/202303231055.DeninwHS-lkp@intel.com/
>  - https://lore.kernel.org/llvm/14c60785-2427-45db-9613-683410ff6802@lucifer.local/T/#t
> 
> 
> --
> Linaro LKFT
> https://lkft.linaro.org
>