linux-kernel - Re: fs/erofs/zdata.c:198:22: sparse: sparse: non size-preserving integer to pointer cast

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Date:   Fri, 7 Aug 2020 22:48:12 +0800
From:   Gao Xiang <hsiangkao@....com>
To:     kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: fs/erofs/zdata.c:198:22: sparse: sparse: non size-preserving
 integer to pointer cast

Hi,

On Fri, Aug 07, 2020 at 08:08:10PM +0800, kernel test robot wrote:
> Hi Gao,
> 
> First bad commit (maybe != root cause):
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   86cfccb66937dd6cbf26ed619958b9e587e6a115
> commit: 47e4937a4a7ca4184fd282791dfee76c6799966a erofs: move erofs out of staging
> date:   12 months ago
> config: s390-randconfig-s032-20200807 (attached as .config)
> compiler: s390-linux-gcc (GCC) 9.3.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # apt-get install sparse
>         # sparse version: v0.6.2-118-ge1578773-dirty
>         git checkout 47e4937a4a7ca4184fd282791dfee76c6799966a
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=s390 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> 
> sparse warnings: (new ones prefixed by >>)
> 
> >> fs/erofs/zdata.c:198:22: sparse: sparse: non size-preserving integer to pointer cast
>    fs/erofs/zdata.c:282:22: sparse: sparse: non size-preserving integer to pointer cast
>    fs/erofs/zdata.c:1094:24: sparse: sparse: non size-preserving integer to pointer cast

I don't think these are valid warnings.

All these three lines are using cmpxchg struct page * (which is equivalent to unsigned long
in these cmpxchg macros) and nothing special at all in my opinion (Especially the last two
lines).

+198	if (!cmpxchg_relaxed(pages, NULL, tagptr_cast_ptr(t)))
+282	if (!cmpxchg(clt->compressedpages++, NULL, page))
+1094	if (oldpage != cmpxchg(&pcl->compressed_pages[nr], oldpage, page)) {

btw, recently sparse warnings quite confuse me (p.s. they're all on alpha/s390/sparc archs and relate
to cmpxchg/xchg by accident), I have no idea what happened with sparse.

Thanks,
Gao Xiang