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* [djwong-xfs:realtime-rmap 245/249] fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here
@ 2020-12-21 19:22 kernel test robot
  2020-12-21 22:19 ` Nathan Chancellor
  0 siblings, 1 reply; 3+ messages in thread
From: kernel test robot @ 2020-12-21 19:22 UTC (permalink / raw)
  To: kbuild-all

[-- Attachment #1: Type: text/plain, Size: 3037 bytes --]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git realtime-rmap
head:   62eb0024d510607ecb04789e8b4f8c0975efb08b
commit: f4188e5ab1984e1b140433a80f223ab4644801af [245/249] xfs: online repair of realtime file bmaps
config: x86_64-randconfig-a011-20201217 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project cee1e7d14f4628d6174b33640d502bff3b54ae45)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?id=f4188e5ab1984e1b140433a80f223ab4644801af
        git remote add djwong-xfs https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git
        git fetch --no-tags djwong-xfs realtime-rmap
        git checkout f4188e5ab1984e1b140433a80f223ab4644801af
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here [-Wuninitialized]
           if (is_free)
               ^~~~~~~
   fs/xfs/scrub/repair.c:2189:16: note: initialize the variable 'is_free' to silence this warning
           bool                    is_free;
                                          ^
                                           = 0
   1 warning generated.


vim +/is_free +2202 fs/xfs/scrub/repair.c

  2173	
  2174	/*
  2175	 * Check if any part of this range of rt blocks is free, so that we don't
  2176	 * rebuild things with bad records.  Returns -EFSCORRUPTED if bad.
  2177	 */
  2178	int
  2179	xrep_rtext_is_free(
  2180		struct xfs_scrub	*sc,
  2181		xfs_rtblock_t		rtbno,
  2182		xfs_filblks_t		len)
  2183	{
  2184		struct xfs_mount	*mp = sc->mp;
  2185		xfs_rtblock_t		startext;
  2186		xfs_rtblock_t		endext;
  2187		xfs_rtblock_t		extcount;
  2188		uint32_t		mod;
  2189		bool			is_free;
  2190		int			error;
  2191	
  2192		/* Convert rt blocks to rt extents. */
  2193		startext = div_u64_rem(rtbno, mp->m_sb.sb_rextsize, &mod);
  2194		endext = div_u64_rem(rtbno + len - 1, mp->m_sb.sb_rextsize, &mod);
  2195	
  2196		/* Make sure this isn't free space. */
  2197		extcount = endext - startext + 1;
  2198		error = xfs_rtalloc_extent_is_free(mp, sc->tp, startext, extcount,
  2199				&is_free);
  2200		if (error)
  2201			return error;
> 2202		if (is_free)
  2203			return -EFSCORRUPTED;
  2204	
  2205		return 0;
  2206	}
  2207	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

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^ permalink raw reply	[flat|nested] 3+ messages in thread
* Re: [djwong-xfs:realtime-rmap 245/249] fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here
  2020-12-21 19:22 [djwong-xfs:realtime-rmap 245/249] fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here kernel test robot
@ 2020-12-21 22:19 ` Nathan Chancellor
  2021-01-04 22:29   ` Darrick J. Wong
  0 siblings, 1 reply; 3+ messages in thread
From: Nathan Chancellor @ 2020-12-21 22:19 UTC (permalink / raw)
  To: kbuild-all

[-- Attachment #1: Type: text/plain, Size: 4348 bytes --]

On Tue, Dec 22, 2020 at 03:22:03AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git realtime-rmap
> head:   62eb0024d510607ecb04789e8b4f8c0975efb08b
> commit: f4188e5ab1984e1b140433a80f223ab4644801af [245/249] xfs: online repair of realtime file bmaps
> config: x86_64-randconfig-a011-20201217 (attached as .config)
> compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project cee1e7d14f4628d6174b33640d502bff3b54ae45)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install x86_64 cross compiling tool for clang build
>         # apt-get install binutils-x86-64-linux-gnu
>         # https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?id=f4188e5ab1984e1b140433a80f223ab4644801af
>         git remote add djwong-xfs https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git
>         git fetch --no-tags djwong-xfs realtime-rmap
>         git checkout f4188e5ab1984e1b140433a80f223ab4644801af
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
> >> fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here [-Wuninitialized]
>            if (is_free)
>                ^~~~~~~
>    fs/xfs/scrub/repair.c:2189:16: note: initialize the variable 'is_free' to silence this warning
>            bool                    is_free;
>                                           ^
>                                            = 0
>    1 warning generated.
> 
> 
> vim +/is_free +2202 fs/xfs/scrub/repair.c
> 
>   2173	
>   2174	/*
>   2175	 * Check if any part of this range of rt blocks is free, so that we don't
>   2176	 * rebuild things with bad records.  Returns -EFSCORRUPTED if bad.
>   2177	 */
>   2178	int
>   2179	xrep_rtext_is_free(
>   2180		struct xfs_scrub	*sc,
>   2181		xfs_rtblock_t		rtbno,
>   2182		xfs_filblks_t		len)
>   2183	{
>   2184		struct xfs_mount	*mp = sc->mp;
>   2185		xfs_rtblock_t		startext;
>   2186		xfs_rtblock_t		endext;
>   2187		xfs_rtblock_t		extcount;
>   2188		uint32_t		mod;
>   2189		bool			is_free;
>   2190		int			error;
>   2191	
>   2192		/* Convert rt blocks to rt extents. */
>   2193		startext = div_u64_rem(rtbno, mp->m_sb.sb_rextsize, &mod);
>   2194		endext = div_u64_rem(rtbno + len - 1, mp->m_sb.sb_rextsize, &mod);
>   2195	
>   2196		/* Make sure this isn't free space. */
>   2197		extcount = endext - startext + 1;
>   2198		error = xfs_rtalloc_extent_is_free(mp, sc->tp, startext, extcount,
>   2199				&is_free);
>   2200		if (error)
>   2201			return error;
> > 2202		if (is_free)
>   2203			return -EFSCORRUPTED;
>   2204	
>   2205		return 0;
>   2206	}
>   2207	
> 
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org
> 

This appears to be a false positive. From the config:

# CONFIG_XFS_RT is not set

which means xfs_rtalloc_extent_is_free evaluates to ENOSYS and we never
actually make it to that if statement evaluation; however, clang cannot
see this because it is doing simple static analysis at this stage of the
pipeline, not seeing that it will never have to use is_free in this
configuration. A simple reproducer:

$ cat test.c
#define func(a) 22

int main() {
    int error;
    _Bool is_free;

    error = func(&is_free);
    if (error)
        return error;
    if (is_free)
        return -117;

    return 0;
}

$ clang -Wuninitialized -fsyntax-only test.c
test.c:10:9: warning: variable 'is_free' is uninitialized when used here [-Wuninitialized]
    if (is_free)
        ^~~~~~~
test.c:5:18: note: initialize the variable 'is_free' to silence this warning
    _Bool is_free;
                 ^
                  = 0
1 warning generated.

Obviously initializing is_free to false will avoid this warning, which
is probably the simplest fix.

Cheers,
Nathan

^ permalink raw reply	[flat|nested] 3+ messages in thread
* Re: [djwong-xfs:realtime-rmap 245/249] fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here
  2020-12-21 22:19 ` Nathan Chancellor
@ 2021-01-04 22:29   ` Darrick J. Wong
  0 siblings, 0 replies; 3+ messages in thread
From: Darrick J. Wong @ 2021-01-04 22:29 UTC (permalink / raw)
  To: kbuild-all

[-- Attachment #1: Type: text/plain, Size: 4966 bytes --]

On Mon, Dec 21, 2020 at 03:19:21PM -0700, Nathan Chancellor wrote:
> On Tue, Dec 22, 2020 at 03:22:03AM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git realtime-rmap
> > head:   62eb0024d510607ecb04789e8b4f8c0975efb08b
> > commit: f4188e5ab1984e1b140433a80f223ab4644801af [245/249] xfs: online repair of realtime file bmaps
> > config: x86_64-randconfig-a011-20201217 (attached as .config)
> > compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project cee1e7d14f4628d6174b33640d502bff3b54ae45)
> > reproduce (this is a W=1 build):
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # install x86_64 cross compiling tool for clang build
> >         # apt-get install binutils-x86-64-linux-gnu
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?id=f4188e5ab1984e1b140433a80f223ab4644801af
> >         git remote add djwong-xfs https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git
> >         git fetch --no-tags djwong-xfs realtime-rmap
> >         git checkout f4188e5ab1984e1b140433a80f223ab4644801af
> >         # save the attached .config to linux build tree
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 
> > 
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@intel.com>
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > >> fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here [-Wuninitialized]
> >            if (is_free)
> >                ^~~~~~~
> >    fs/xfs/scrub/repair.c:2189:16: note: initialize the variable 'is_free' to silence this warning
> >            bool                    is_free;
> >                                           ^
> >                                            = 0
> >    1 warning generated.
> > 
> > 
> > vim +/is_free +2202 fs/xfs/scrub/repair.c
> > 
> >   2173	
> >   2174	/*
> >   2175	 * Check if any part of this range of rt blocks is free, so that we don't
> >   2176	 * rebuild things with bad records.  Returns -EFSCORRUPTED if bad.
> >   2177	 */
> >   2178	int
> >   2179	xrep_rtext_is_free(
> >   2180		struct xfs_scrub	*sc,
> >   2181		xfs_rtblock_t		rtbno,
> >   2182		xfs_filblks_t		len)
> >   2183	{
> >   2184		struct xfs_mount	*mp = sc->mp;
> >   2185		xfs_rtblock_t		startext;
> >   2186		xfs_rtblock_t		endext;
> >   2187		xfs_rtblock_t		extcount;
> >   2188		uint32_t		mod;
> >   2189		bool			is_free;
> >   2190		int			error;
> >   2191	
> >   2192		/* Convert rt blocks to rt extents. */
> >   2193		startext = div_u64_rem(rtbno, mp->m_sb.sb_rextsize, &mod);
> >   2194		endext = div_u64_rem(rtbno + len - 1, mp->m_sb.sb_rextsize, &mod);
> >   2195	
> >   2196		/* Make sure this isn't free space. */
> >   2197		extcount = endext - startext + 1;
> >   2198		error = xfs_rtalloc_extent_is_free(mp, sc->tp, startext, extcount,
> >   2199				&is_free);
> >   2200		if (error)
> >   2201			return error;
> > > 2202		if (is_free)
> >   2203			return -EFSCORRUPTED;
> >   2204	
> >   2205		return 0;
> >   2206	}
> >   2207	
> > 
> > ---
> > 0-DAY CI Kernel Test Service, Intel Corporation
> > https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org
> > 
> 
> This appears to be a false positive. From the config:
> 
> # CONFIG_XFS_RT is not set
> 
> which means xfs_rtalloc_extent_is_free evaluates to ENOSYS and we never
> actually make it to that if statement evaluation; however, clang cannot
> see this because it is doing simple static analysis at this stage of the
> pipeline, not seeing that it will never have to use is_free in this
> configuration. A simple reproducer:
> 
> $ cat test.c
> #define func(a) 22
> 
> int main() {
>     int error;
>     _Bool is_free;
> 
>     error = func(&is_free);
>     if (error)
>         return error;
>     if (is_free)
>         return -117;
> 
>     return 0;
> }
> 
> $ clang -Wuninitialized -fsyntax-only test.c
> test.c:10:9: warning: variable 'is_free' is uninitialized when used here [-Wuninitialized]
>     if (is_free)
>         ^~~~~~~
> test.c:5:18: note: initialize the variable 'is_free' to silence this warning
>     _Bool is_free;
>                  ^
>                   = 0
> 1 warning generated.
> 
> Obviously initializing is_free to false will avoid this warning, which
> is probably the simplest fix.

I don't mind making that change (and in fact already did), but uh...
shouldn't clang be analyzing the C source code /after/ the preprocessing
step?  I bet there's a fair amount of #define soup in the kernel that
clang would /love/ to sink its teeth into. ;)

Insofar as one doesn't need teeth for soup.

--D

> Cheers,
> Nathan

^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-01-04 22:29 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-12-21 19:22 [djwong-xfs:realtime-rmap 245/249] fs/xfs/scrub/repair.c:2202:6: warning: variable 'is_free' is uninitialized when used here kernel test robot
2020-12-21 22:19 ` Nathan Chancellor
2021-01-04 22:29   ` Darrick J. Wong

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