[linux-next:master 11586/13643] fs/debugfs/file.c:942:9: sparse: sparse: incompatible types in comparison expression (different address spaces):

[kernel test robot <lkp@xxxxxxxxx>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   a47fc304d2b678db1a5d760a7d644dac9b067752
commit: 86b5488121db563b33684f56aafa62156f764be3 [11586/13643] debugfs: Add write support to debugfs_create_str()
config: i386-randconfig-061-20230901 (https://download.01.org/0day-ci/archive/20230901/202309011707.9Xv56Ryt-lkp@xxxxxxxxx/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230901/202309011707.9Xv56Ryt-lkp@xxxxxxxxx/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@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309011707.9Xv56Ryt-lkp@xxxxxxxxx/

sparse warnings: (new ones prefixed by >>)
>> fs/debugfs/file.c:942:9: sparse: sparse: incompatible types in comparison expression (different address spaces):
>> fs/debugfs/file.c:942:9: sparse:    char [noderef] __rcu *
>> fs/debugfs/file.c:942:9: sparse:    char *

vim +942 fs/debugfs/file.c

   903	
   904	static ssize_t debugfs_write_file_str(struct file *file, const char __user *user_buf,
   905					      size_t count, loff_t *ppos)
   906	{
   907		struct dentry *dentry = F_DENTRY(file);
   908		char *old, *new = NULL;
   909		int pos = *ppos;
   910		int r;
   911	
   912		r = debugfs_file_get(dentry);
   913		if (unlikely(r))
   914			return r;
   915	
   916		old = *(char **)file->private_data;
   917	
   918		/* only allow strict concatenation */
   919		r = -EINVAL;
   920		if (pos && pos != strlen(old))
   921			goto error;
   922	
   923		r = -E2BIG;
   924		if (pos + count + 1 > PAGE_SIZE)
   925			goto error;
   926	
   927		r = -ENOMEM;
   928		new = kmalloc(pos + count + 1, GFP_KERNEL);
   929		if (!new)
   930			goto error;
   931	
   932		if (pos)
   933			memcpy(new, old, pos);
   934	
   935		r = -EFAULT;
   936		if (copy_from_user(new + pos, user_buf, count))
   937			goto error;
   938	
   939		new[pos + count] = '\0';
   940		strim(new);
   941	
 > 942		rcu_assign_pointer(*(char **)file->private_data, new);
   943		synchronize_rcu();
   944		kfree(old);
   945	
   946		debugfs_file_put(dentry);
   947		return count;
   948	
   949	error:
   950		kfree(new);
   951		debugfs_file_put(dentry);
   952		return r;
   953	}
   954	

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