Re: [RFC PATCH 1/5] fs: introduce notifier list for vfs inode

[Amir Goldstein <amir73il@gmail.com>]

> Very well, I will try to explain with code:
>
> int ovl_inode_is_open_for_write(struct inode *inode)
> {
>        struct inode *upper_inode = ovl_inode_upper(inode);
>
>        return upper_inode && inode_is_open_for_write(upper_inode);
> }
>
> void ovl_maybe_mark_inode_dirty(struct inode *inode)
> {
>        struct inode *upper_inode = ovl_inode_upper(inode);
>
>        if (upper_inode && upper_inode->i_state & I_DIRTY_ALL)
>                 mark_inode_dirty(inode);
> }
>
> int ovl_open(struct inode *inode, struct file *file)
> {
> ...
>        if (ovl_inode_is_open_for_write(file_inode(file)))
>                ovl_add_inode_to_suspect_list(inode);
>
>         file->private_data = realfile;
>
>         return 0;
> }
>
> int ovl_release(struct inode *inode, struct file *file)
> {
>        struct inode *inode = file_inode(file);
>
>        if (ovl_inode_is_open_for_write(inode)) {

Darn! that should have been (!ovl_inode_is_open_for_write(inode))
and it should be done after fput() and grabbing inode reference with
ihold() before fput().

>                ovl_maybe_mark_inode_dirty(inode);
>                ovl_remove_inode_from_suspect_list(inode);
>        }
>
>         fput(file->private_data);
>
>         return 0;
> }
>
> int ovl_drop_inode(struct inode *inode)
> {
>        struct inode *upper_inode = ovl_inode_upper(inode);
>
>        if (!upper_inode)
>                return 1;
>        if (upper_inode->i_state & I_DIRTY_ALL)
>                return 0;
>
>        return !inode_is_open_for_write(upper_inode);
> }
>
> static int ovl_sync_fs(struct super_block *sb, int wait)
> {
>         struct ovl_fs *ofs = sb->s_fs_info;
>         struct super_block *upper_sb;
>         int ret;
>
>         if (!ovl_upper_mnt(ofs))
>                 return 0;
>
>         /*
>          * Not called for sync(2) call or an emergency sync (SB_I_SKIP_SYNC).
>          * All the super blocks will be iterated, including upper_sb.
>          *
>          * If this is a syncfs(2) call, then we do need to call
>          * sync_filesystem() on upper_sb, but enough if we do it when being
>          * called with wait == 1.
>          */
>         if (!wait) {
>                 /* mark inodes on the suspect list dirty if thier
> upper inode is dirty */
>                 ovl_mark_suspect_list_inodes_dirty();
>                 return 0;
>         }
> ...
>
>
> The races are avoided because inode is added/removed from suspect
> list while overlay inode has a reference (from file) and because upper inode
> cannot be dirtied by overlayfs when overlay inode is not on the suspect list.
>
> Unless I am missing something.
>
> Thanks,
> Amir.