ebiederm@xxxxxxxxxxxx (Eric W. Biederman) writes: > Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx> writes: > >> Gents, >> >> I wondered if a naive solution could re-walk the list of mounts >> processed in umount_tree() and if all of the detached but locked mounts >> had a refcount that indicated they're unused, they could be unlocked and >> unmounted. At least in the case of the containers I'm dealing with, the >> the container software should be ensuring that nothing in the container >> has a reference on anything that's under the detached portion of the >> tree. However, there's probably a better way to do this. > > So if the code is working correctly that should already happen. > > The design is for the parent mount to hold a reference to the submounts. > And when the reference on the parent drops to 0. The references on > all of the submounts will also be dropped. > > I was hoping to read the code and point it out to you quickly, but I am > not seeing it now. I am wondering if in all of the refactoring of that > code something was dropped/missed :( > > Somewhere there is supposed to be the equivalent of: > pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt, &unmounted); > when we unhash those mounts because the last count has gone away. > Either it is very sophisticated or I am missing it. Grr.... Ok. I see the code now, and it should be doing the right thing. During umount_tree the code calls pin_insert_group(...) with the last paramenter being NULL. That adds the mount to one or two lists. The mnt_pins list of the parent mount and the &unmounted hlist. Then later when the parent's cleanup_mnt is called if the mnt_pins still has entries mnt_pin_kill is called. For every mount on the mnt_pins list drop_mountpoint is called. Which calls dput and mntput. So that is how your references are supposed to be freed. Which leaves the question why aren't your mounts being freed? Is a file descriptor perhaps from a mmaped executable holding a mount reference? Perhaps you want to manually unmount everything and see if unmount will fail on some mount and let you see which mount has a reference to it. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
