vfs: remove redundant checks from generic_remap_checks()

The access limit checks on input file range in generic_remap_checks()
are redundant because the input file size is guaranteed to be within
limits and pos+len are already checked to be within input file size.

Beyond the fact that the check cannot fail, if it would have failed,
it could return -EFBIG for input file range error. There is no precedent
for that. -EFBIG is returned in syscalls that would change file length.

With that call removed, we can fold generic_access_check_limits() into
generic_write_check_limits().

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/mm/filemap.c b/mm/filemap.c
index a38619a..4436192 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2895,24 +2895,11 @@ EXPORT_SYMBOL(read_cache_page_gfp);
  * LFS limits.  If pos is under the limit it becomes a short access.  If it
  * exceeds the limit we return -EFBIG.
  */
-static int generic_access_check_limits(struct file *file, loff_t pos,
-                                      loff_t *count)
-{
-       struct inode *inode = file->f_mapping->host;
-       loff_t max_size = inode->i_sb->s_maxbytes;
-
-       if (!(file->f_flags & O_LARGEFILE))
-               max_size = MAX_NON_LFS;
-
-       if (unlikely(pos >= max_size))
-               return -EFBIG;
-       *count = min(*count, max_size - pos);
-       return 0;
-}
-
 static int generic_write_check_limits(struct file *file, loff_t pos,
                                      loff_t *count)
 {
+       struct inode *inode = file->f_mapping->host;
+       loff_t max_size = inode->i_sb->s_maxbytes;
        loff_t limit = rlimit(RLIMIT_FSIZE);
 
        if (limit != RLIM_INFINITY) {
@@ -2923,7 +2910,15 @@ static int generic_write_check_limits(struct file *file, loff_t pos,
                *count = min(*count, limit - pos);
        }
 
-       return generic_access_check_limits(file, pos, count);
+       if (!(file->f_flags & O_LARGEFILE))
+               max_size = MAX_NON_LFS;
+
+       if (unlikely(pos >= max_size))
+               return -EFBIG;
+
+       *count = min(*count, max_size - pos);
+
+       return 0;
 }
 
 /*
@@ -2963,7 +2958,7 @@ EXPORT_SYMBOL(generic_write_checks);
 /*
  * Performs necessary checks before doing a clone.
  *
- * Can adjust amount of bytes to clone.
+ * Can adjust amount of bytes to clone via @req_count argument.
  * Returns appropriate error code that caller should return or
  * zero in case the clone should be allowed.
  */
@@ -3001,10 +2996,6 @@ int generic_remap_checks(struct file *file_in, loff_t pos_in,
                return -EINVAL;
        count = min(count, size_in - (uint64_t)pos_in);
 
-       ret = generic_access_check_limits(file_in, pos_in, &count);
-       if (ret)
-               return ret;
-
        ret = generic_write_check_limits(file_out, pos_out, &count);
        if (ret)
                return ret;