Re: [PATCH -next V2] proc: support file->f_pos checking in mem_lseek

[kernel test robot <lkp@intel.com>]

Hi WoZ1zh1,

kernel test robot noticed the following build warnings:

[auto build test WARNING on next-20231108]

url:    https://github.com/intel-lab-lkp/linux/commits/WoZ1zh1/proc-support-file-f_pos-checking-in-mem_lseek/20231109-103353
base:   next-20231108
patch link:    https://lore.kernel.org/r/20231109102658.2075547-1-wozizhi%40huawei.com
patch subject: [PATCH -next V2] proc: support file->f_pos checking in mem_lseek
config: arc-randconfig-001-20231109 (https://download.01.org/0day-ci/archive/20231109/202311091307.k2L6reDL-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231109/202311091307.k2L6reDL-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202311091307.k2L6reDL-lkp@intel.com/

All warnings (new ones prefixed by >>):

   fs/proc/base.c: In function 'mem_lseek':
>> fs/proc/base.c:911:24: warning: this statement may fall through [-Wimplicit-fallthrough=]
     911 |                 offset += file->f_pos;
         |                 ~~~~~~~^~~~~~~~~~~~~~
   fs/proc/base.c:912:9: note: here
     912 |         case SEEK_SET:
         |         ^~~~


vim +911 fs/proc/base.c

   903	
   904	loff_t mem_lseek(struct file *file, loff_t offset, int orig)
   905	{
   906		loff_t ret = 0;
   907	
   908		spin_lock(&file->f_lock);
   909		switch (orig) {
   910		case SEEK_CUR:
 > 911			offset += file->f_pos;
   912		case SEEK_SET:
   913			/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
   914			if ((unsigned long long)offset >= -MAX_ERRNO)
   915				ret = -EOVERFLOW;
   916			break;
   917		default:
   918			ret = -EINVAL;
   919		}
   920		if (!ret) {
   921			if (offset < 0 && !(unsigned_offsets(file))) {
   922				ret = -EINVAL;
   923			} else {
   924				file->f_pos = offset;
   925				ret = file->f_pos;
   926				force_successful_syscall_return();
   927			}
   928		}
   929	
   930		spin_unlock(&file->f_lock);
   931		return ret;
   932	}
   933	

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https://github.com/intel/lkp-tests/wiki