Re: [PATCH] mm/mremap: fix uninitialized return code

["Arnd Bergmann" <arnd@arndb.de>]

On Wed, Mar 5, 2025, at 18:29, Lorenzo Stoakes wrote:
> On Wed, Mar 05, 2025 at 06:27:56PM +0100, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>>
>> The 'err' variable is set in a conditinal branch and is not
>> set otherwise:
>>
>> mm/mremap.c:1017:7: error: variable 'err' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>>  1017 |                 if (vma->vm_start != old_addr)
>>
>> Set it to zero before the initial value is set.
>>
>> Fixes: 3129f7896afb ("mm/mremap: initial refactor of move_vma()")
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> Thanks for this, however this has already been fixed via Andrew doing a
> fix-patch which should land in mm-unstable,-next soon (possibly tmr?).
>
> This is entirely my bad btw, for some reason my compiler locally didn't
> catch this even with CONFIG_WERROR on which _really_ surprises me...

Unfortunately gcc never shows warnings about conditionally uninitialized
variables. There is a -Wmaybe-uninitialized, but that has so many
false positives that it is completely useless and it is turned
off globally.

      Arnd