Re: [linux-next:master 5025/9010] tcp_mmap.c:211:61: warning: 'lu' may be used uninitialized in this function

[Eric Dumazet <edumazet@google.com>]

On Tue, Apr 4, 2023 at 4:10 PM kernel test robot <lkp@intel.com> wrote:
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   6a53bda3aaf3de5edeea27d0b1d8781d067640b6
> commit: 5c5945dc695c54f2b55a934a10b6c4e220f9c140 [5025/9010] selftests/net: Add SHA256 computation over data sent in tcp_mmap
> compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
> reproduce:
>         # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=5c5945dc695c54f2b55a934a10b6c4e220f9c140
>         git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>         git fetch --no-tags linux-next master
>         git checkout 5c5945dc695c54f2b55a934a10b6c4e220f9c140
>         make O=/tmp/kselftest headers
>         make O=/tmp/kselftest -C tools/testing/selftests
>
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
> | Link: https://lore.kernel.org/oe-kbuild-all/202304042104.UFIuevBp-lkp@intel.com/
>
> Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
> http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings
>
> All warnings (new ones prefixed by >>):
>
>    tcp_mmap.c: In function 'child_thread':
> >> tcp_mmap.c:211:61: warning: 'lu' may be used uninitialized in this function [-Wmaybe-uninitialized]
>      211 |                         zc.length = min(chunk_size, FILE_SZ - lu);
>          |                                                             ^


This is not a false warning, I will submit this fix, thanks.

diff --git a/tools/testing/selftests/net/tcp_mmap.c
b/tools/testing/selftests/net/tcp_mmap.c
index 607cc9ad8d1b72cdcb96ca0d6fdb70900c9b9bc0..6e59b1461dcceaa658185071a758e1006b48299a
100644
--- a/tools/testing/selftests/net/tcp_mmap.c
+++ b/tools/testing/selftests/net/tcp_mmap.c
@@ -208,7 +208,7 @@ void *child_thread(void *arg)

                        memset(&zc, 0, sizeof(zc));
                        zc.address = (__u64)((unsigned long)addr);
-                       zc.length = min(chunk_size, FILE_SZ - lu);
+                       zc.length = min(chunk_size, FILE_SZ - total);

                        res = getsockopt(fd, IPPROTO_TCP, TCP_ZEROCOPY_RECEIVE,
                                         &zc, &zc_len);