linux-kernel - Re: net/ceph/osdmap.c:1246:10: warning: result of comparison of constant 4611686018427387891 with expression of type 'u32' (aka 'unsigned int') is always false

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Date:   Mon, 6 Nov 2023 08:50:38 +0800
From:   Philip Li <philip.li@...el.com>
To:     kernel test robot <lkp@...el.com>
CC:     Nathan Chancellor <natechancellor@...il.com>,
        <llvm@...ts.linux.dev>, <oe-kbuild-all@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>,
        "Masahiro Yamada" <masahiroy@...nel.org>
Subject: Re: net/ceph/osdmap.c:1246:10: warning: result of comparison of
 constant 4611686018427387891 with expression of type 'u32' (aka 'unsigned
 int') is always false

On Mon, Nov 06, 2023 at 07:13:50AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   77fa2fbe87fc605c4bfa87dff87be9bfded0e9a3
> commit: afe956c577b2d5a3d9834e4424587c1ebcf90c4c kbuild: Enable -Wtautological-compare
> date:   3 years, 7 months ago
> config: x86_64-randconfig-012-20230909 (https://download.01.org/0day-ci/archive/20231106/202311060731.8P11QmUf-lkp@intel.com/config)
> compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231106/202311060731.8P11QmUf-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202311060731.8P11QmUf-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):

Sorry for wrong report, kindly ignore this, it bisects to wrong commit that is
not the real cause.

> 
>    net/ceph/osdmap.c:176:6: warning: no previous prototype for function 'clear_choose_args' [-Wmissing-prototypes]
>    void clear_choose_args(struct crush_map *c)
>         ^
>    net/ceph/osdmap.c:176:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
>    void clear_choose_args(struct crush_map *c)
>    ^
>    static 
> >> net/ceph/osdmap.c:1246:10: warning: result of comparison of constant 4611686018427387891 with expression of type 'u32' (aka 'unsigned int') is always false [-Wtautological-constant-out-of-range-compare]
>            if (len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
>                ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    net/ceph/osdmap.c:1429:10: warning: result of comparison of constant 2305843009213693945 with expression of type 'u32' (aka 'unsigned int') is always false [-Wtautological-constant-out-of-range-compare]
>            if (len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
>                ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    3 warnings generated.
> --
> >> drivers/block/rbd.c:6190:17: warning: result of comparison of constant 2305843009213693948 with expression of type 'u32' (aka 'unsigned int') is always false [-Wtautological-constant-out-of-range-compare]
>            if (snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context))
>                ~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    1 warning generated.
> 
> 
> vim +1246 net/ceph/osdmap.c
> 
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1236  
> a303bb0e58345f Ilya Dryomov 2017-06-21  1237  static struct ceph_pg_mapping *__decode_pg_temp(void **p, void *end,
> a303bb0e58345f Ilya Dryomov 2017-06-21  1238  						bool incremental)
> a303bb0e58345f Ilya Dryomov 2017-06-21  1239  {
> a303bb0e58345f Ilya Dryomov 2017-06-21  1240  	struct ceph_pg_mapping *pg;
> a303bb0e58345f Ilya Dryomov 2017-06-21  1241  	u32 len, i;
> a303bb0e58345f Ilya Dryomov 2017-06-21  1242  
> a303bb0e58345f Ilya Dryomov 2017-06-21  1243  	ceph_decode_32_safe(p, end, len, e_inval);
> a303bb0e58345f Ilya Dryomov 2017-06-21  1244  	if (len == 0 && incremental)
> a303bb0e58345f Ilya Dryomov 2017-06-21  1245  		return NULL;	/* new_pg_temp: [] to remove */
> a303bb0e58345f Ilya Dryomov 2017-06-21 @1246  	if (len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
> a303bb0e58345f Ilya Dryomov 2017-06-21  1247  		return ERR_PTR(-EINVAL);
> a303bb0e58345f Ilya Dryomov 2017-06-21  1248  
> a303bb0e58345f Ilya Dryomov 2017-06-21  1249  	ceph_decode_need(p, end, len * sizeof(u32), e_inval);
> a303bb0e58345f Ilya Dryomov 2017-06-21  1250  	pg = alloc_pg_mapping(len * sizeof(u32));
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1251  	if (!pg)
> a303bb0e58345f Ilya Dryomov 2017-06-21  1252  		return ERR_PTR(-ENOMEM);
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1253  
> 35a935d75d51ab Ilya Dryomov 2014-03-21  1254  	pg->pg_temp.len = len;
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1255  	for (i = 0; i < len; i++)
> 35a935d75d51ab Ilya Dryomov 2014-03-21  1256  		pg->pg_temp.osds[i] = ceph_decode_32(p);
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1257  
> a303bb0e58345f Ilya Dryomov 2017-06-21  1258  	return pg;
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1259  
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1260  e_inval:
> a303bb0e58345f Ilya Dryomov 2017-06-21  1261  	return ERR_PTR(-EINVAL);
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1262  }
> 10db634e2083a2 Ilya Dryomov 2014-03-21  1263  
> 
> :::::: The code at line 1246 was first introduced by commit
> :::::: a303bb0e58345fe9f7ab2f82b90266f2b5036058 libceph: introduce and switch to decode_pg_mapping()
> 
> :::::: TO: Ilya Dryomov <idryomov@...il.com>
> :::::: CC: Ilya Dryomov <idryomov@...il.com>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki