[PATCH, RFC] Ext4: Mount partition as read only if during orphan cleanup truncate fails to obtain journal handle.

During orphan cleanup while doing truncate, if we fail to obtain journal
handle, the inode for which truncate was called would not be removed from
both the on-disk and in-memory orphan lists as the call to ext4_orphan_del
would not be executed.

This would have following consequences:
a) As the inode is not removed from the on-disk list, truncate would be 
called again for the same inode. Each call would add the inode to the
in-memory list. This operation would continue endlessly or until truncate
is succeed.

b) If somehow, after some iterations, truncate is succeed, ext4_orphan_del
will only remove the inode from in-memory list just 1 time. This will trigger
j_assert during put super.

This patch handles both the problems. If truncate fails, first in-memory
list is cleared and than the partition is mounted as read only.
Failure to obtain journal handle during mount may suggest that journal
device is corrupted.

Signed-off-by: Ashish Sangwan <redacted>
Signed-off-by: Namjae Jeon <redacted> 
---
 fs/ext4/super.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4e2aacb..859eccb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c

@@ -2201,7 +2201,21 @@ static void ext4_orphan_cleanup(struct super_block *sb,
 			jbd_debug(2, "truncating inode %lu to %lld bytes\n",
 				  inode->i_ino, inode->i_size);
 			ext4_truncate(inode);
-			nr_truncates++;
+			if (list_empty(&EXT4_I(inode)->i_orphan)) {
+				nr_truncates++;
+			} else {
+				/* Remove inode from in-memory orphan list */
+				list_del_init(&EXT4_I(inode)->i_orphan);
+				ext4_msg(sb, KERN_ERR, "Truncate failed for "
+					 "orphan  inode = %lu. Running e2fsck"
+					 " is recommended", inode->i_ino);
+				if (!(s_flags & MS_RDONLY)) {
+					ext4_msg(sb, KERN_INFO, "FS would be"
+						" mounted as readonly");
+					s_flags |= MS_RDONLY;
+				}
+				break;
+			}
 		} else {
 			ext4_msg(sb, KERN_DEBUG,
 				"%s: deleting unreferenced inode %lu",

-- 
1.7.11.4