linux-kernel - Re: mm/vmalloc.c:4691:25: error: variable 'addr' is uninitialized when used here [-Werror,-Wuninitialized]

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Date: Fri, 12 Jan 2024 13:46:22 +1100
From: Stephen Rothwell <sfr@...b.auug.org.au>
To: "Arnd Bergmann" <arnd@...db.de>
Cc: "Dan Carpenter" <dan.carpenter@...aro.org>, "Naresh Kamboju"
 <naresh.kamboju@...aro.org>, "Uladzislau Rezki" <urezki@...il.com>,
 linux-next <linux-next@...r.kernel.org>, "open list"
 <linux-kernel@...r.kernel.org>, "Linux Regressions"
 <regressions@...ts.linux.dev>, clang-built-linux <llvm@...ts.linux.dev>,
 lkft-triage@...ts.linaro.org, "Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: mm/vmalloc.c:4691:25: error: variable 'addr' is uninitialized
 when used here [-Werror,-Wuninitialized]

Hi all,

On Thu, 11 Jan 2024 17:37:12 +0100 "Arnd Bergmann" <arnd@...db.de> wrote:
>
> On Thu, Jan 11, 2024, at 13:55, Arnd Bergmann wrote:
> > On Thu, Jan 11, 2024, at 12:16, Dan Carpenter wrote:  
> >> On Thu, Jan 11, 2024 at 04:23:09PM +0530, Naresh Kamboju wrote:  
> >>> Following build failures noticed on i386 and x86 with clang builds on the
> >>> Linux next-20240111 tag.
> >>> 
> >>> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> >>> 
> >>> Build error:
> >>> ----------
> >>> mm/vmalloc.c:4691:25: error: variable 'addr' is uninitialized when
> >>> used here [-Werror,-Wuninitialized]
> >>>  4691 |                 va = __find_vmap_area(addr, &vn->busy.root);
> >>>       |                                       ^~~~
> >>> mm/vmalloc.c:4684:20: note: initialize the variable 'addr' to silence
> >>> this warning
> >>>  4684 |         unsigned long addr;
> >>>       |                           ^
> >>>       |                            = 0
> >>> 1 error generated.  
> >>
> >> We turned off uninitialized variable warnings for GCC a long time ago..
> >> :/ I don't know if we'll be able to re-enable it in a -Werror world
> >> although Clang seems to be managing alright so perhaps there is hope.  
> >
> > The problem with gcc's warning is that it is non-deterministic and
> > in recent versions actually got more false-positives even without
> > -Os or -fsanitize=. Clang does not catch all that gcc does because
> > it doesn't track state across inline functions, but at least its
> > output is always the same regardless of optimization and other
> > options.
> >
> > At least this particular one is an obvious bug and easily gets
> > caught by lkft and lkp even if gcc's -Wuninitilized doesn't
> > flag it.  
> 
> As it turns out, gcc did find this one in the default -Wuninitialized
> regardless of -Wmaybe-uninitialized:
> 
> mm/vmalloc.c: In function 'vmalloc_dump_obj':
> mm/vmalloc.c:4691:22: error: 'addr' is used uninitialized [-Werror=uninitialized]
>  4691 |                 va = __find_vmap_area(addr, &vn->busy.root);
>       |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/vmalloc.c:4684:23: note: 'addr' was declared here
>  4684 |         unsigned long addr;
>       |                       ^~~~
> 
> and I see that Uladzislau Rezki already sent a fix, which
> is the same that I tried out in my randconfig tree:
> https://lore.kernel.org/lkml/ZaARXdbigD1hWuOS@pc638.lan/

I have applied that to linux-next today.

-- 
Cheers,
Stephen Rothwell

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