f2fs: add f2fs_bug_on() in f2fs_quota_read()

mapping_read_folio_gfp() will return a folio, it should always be
uptodate, let's check folio uptodate status to detect any potenial
bug.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/super.c

@@ -2734,6 +2734,12 @@ static ssize_t f2fs_quota_read(struct super_block *sb, int type, char *data,
 			goto repeat;
 		}
 
+		/*
+		 * should never happen, just leave f2fs_bug_on() here to catch
+		 * any potential bug.
+		 */
+		f2fs_bug_on(F2FS_SB(sb), !folio_test_uptodate(folio));
+
 		memcpy_from_folio(data, folio, offset, tocopy);
 		f2fs_folio_put(folio, true);