[amir73il:ovl_real_file 2/4] fs/overlayfs/file.c:139:23: sparse: sparse: Using plain integer as NULL pointer

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

tree:   https://github.com/amir73il/linux ovl_real_file
head:   2e6c8d603136baf0de510ba069ad78a449012807
commit: e37f0a8ea49c2287a7c722abb1d4d97619bc7271 [2/4] ovl: stash upper real file in backing_file struct
config: hexagon-randconfig-r113-20241005 (https://download.01.org/0day-ci/archive/20241006/202410060829.UTwmlmcr-lkp@intel.com/config)
compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project fef3566a25ff0e34fb87339ba5e13eca17cec00f)
reproduce: (https://download.01.org/0day-ci/archive/20241006/202410060829.UTwmlmcr-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/202410060829.UTwmlmcr-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> fs/overlayfs/file.c:139:23: sparse: sparse: Using plain integer as NULL pointer

vim +139 fs/overlayfs/file.c

    93	
    94	static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
    95				       bool upper_meta)
    96	{
    97		struct dentry *dentry = file_dentry(file);
    98		struct file *realfile = file->private_data;
    99		struct file *upperfile = backing_file_private(realfile);
   100		struct path realpath;
   101		int err;
   102	
   103		real->word = 0;
   104	
   105		if (upper_meta) {
   106			ovl_path_upper(dentry, &realpath);
   107			if (!realpath.dentry)
   108				return 0;
   109		} else {
   110			/* lazy lookup and verify of lowerdata */
   111			err = ovl_verify_lowerdata(dentry);
   112			if (err)
   113				return err;
   114	
   115			ovl_path_realdata(dentry, &realpath);
   116		}
   117		if (!realpath.dentry)
   118			return -EIO;
   119	
   120	stashed_upper:
   121		if (upperfile && file_inode(upperfile) == d_inode(realpath.dentry))
   122			realfile = upperfile;
   123	
   124		/*
   125		 * If realfile is lower and has been copied up since we'd opened it,
   126		 * open the real upper file and stash it in backing_file_private().
   127		 */
   128		if (unlikely(file_inode(realfile) != d_inode(realpath.dentry))) {
   129			struct file *old;
   130	
   131			/* Stashed upperfile has a mismatched inode */
   132			if (unlikely(upperfile))
   133				return -EIO;
   134	
   135			upperfile = ovl_open_realfile(file, &realpath);
   136			if (IS_ERR(upperfile))
   137				return PTR_ERR(upperfile);
   138	
 > 139			old = cmpxchg_release(backing_file_private_ptr(realfile), NULL,
   140					      upperfile);
   141			if (old) {
   142				fput(upperfile);
   143				upperfile = old;
   144			}
   145	
   146			goto stashed_upper;
   147		}
   148	
   149		real->word = (unsigned long)realfile;
   150	
   151		/* Did the flags change since open? */
   152		if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS))
   153			return ovl_change_flags(realfile, file->f_flags);
   154	
   155		return 0;
   156	}
   157	

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