ocfs2: no need try to truncate file beyond i_size

Linux fallocate(2) with FALLOC_FL_PUNCH_HOLE mode set, its offset can
exceed the inode size.  Ocfs2 now doesn't allow that offset beyond inode
size.  This restriction is not necessary and violates fallocate(2)
semantics.

If fallocate(2) offset is beyond inode size, just return success and do
nothing further.

Otherwise, ocfs2 will crash the kernel.

  kernel BUG at fs/ocfs2//alloc.c:7264!
   ocfs2_truncate_inline+0x20f/0x360 [ocfs2]
   ocfs2_remove_inode_range+0x23c/0xcb0 [ocfs2]
   __ocfs2_change_file_space+0x4a5/0x650 [ocfs2]
   ocfs2_fallocate+0x83/0xa0 [ocfs2]
   vfs_fallocate+0x148/0x230
   SyS_fallocate+0x48/0x80
   do_syscall_64+0x79/0x170

Signed-off-by: Changwei Ge <chge@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200407082754.17565-1-chge@linux.alibaba.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index 65b3abb..2f834ad 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -7402,6 +7402,10 @@
 	struct ocfs2_dinode *di = (struct ocfs2_dinode *)di_bh->b_data;
 	struct ocfs2_inline_data *idata = &di->id2.i_data;
 
+	/* No need to punch hole beyond i_size. */
+	if (start >= i_size_read(inode))
+		return 0;
+
 	if (end > i_size_read(inode))
 		end = i_size_read(inode);