linux-kernel - 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 13:28:10 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     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>
Subject: mm/mmap.c:939:11: error: variable 'next' is used uninitialized
 whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]

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
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