On Fri, May 25, 2018 at 01:07:34AM +0100, David Howells wrote:
> + if (unlikely(file->f_mode & FMODE_NEED_UNMOUNT))
> + __detach_mounts(dentry);
> +
This is completely wrong. First of all, you want to dissolve the mount tree
on file->f_path.mount, not every tree rooted at dentry equal to file->f_path.dentry.
This is easily done - it would be a simple call of drop_collected_mounts(mnt)
if not for one detail. You want it to happen only if the sucker isn't attached
anywhere by that point. IOW,
namespace_lock();
lock_mount_hash();
if (!real_mount(mnt)->mnt_ns)
umount_tree(real_mount(mnt), UMOUNT_SYNC);
unlock_mount_hash();
namespace_unlock();
and that's it. You don't need that magical mystery turd in move_mount() later
in the series and all the infrastructure you grow for it.
FWIW, I would've suggested this
void drop_collected_mounts(struct vfsmount *mnt)
{
namespace_lock();
lock_mount_hash();
+ if (!real_mount(mnt)->mnt_ns)
+ umount_tree(real_mount(mnt), UMOUNT_SYNC);
- umount_tree(real_mount(mnt), UMOUNT_SYNC);
unlock_mount_hash();
namespace_unlock();
}
and in __fput()
if (unlikely(file->f_mode & FMODE_NEED_UNMOUNT))
drop_collected_mounts(mnt);
All there is to it, AFAICS...
