On Tue, Jun 10, 2025 at 09:17:58AM +0100, Al Viro wrote: > The next pile of mount massage; it will grow - there will be > further modifications, as well as fixes and documentation, but this is > the subset I've got in more or less settled form right now. > > Review and testing would be very welcome. > > This series (-rc1-based) sits in > git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #work.mount > individual patches in followups. Updated variant force-pushed to git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #work.mount individual patches in followups. It seems to survive testing here, but more testing and review would be very welcome. That's still not all - there's more stuff in local queue, but it needs more massage; this is the reasonably settled-down subset at the moment. Changes since v1: Added fixes (-stable fodder, IMO): replace collect_mounts()/drop_collected_mounts() with safer variant attach_recursive_mnt(): do not lock the covering tree when sliding something under it Another thing that is probably a -stable candidate: prevent mount hash conflicts That's an old headache hopefully taken care of; what we get out of it is the warranty that there won't be more than one hashed mount with given parent/mountpoint at any given time. I've pulled that very early in the sequence, so that we had a chance to backport it. That comes with two prereqs (reordered from the middle of v1 series), both should be trivial to backport. Added cleanups: __attach_mnt(): lose the second argument copy_tree(): don't link the mounts via mnt_list All uses of ->mnt_list are transient now - basically, various sets used during umount_tree(). mount: separate the flags accessed only under namespace_sem Makes for simpler locking; some of the flags are accessed only under namespace_sem, and we already rely upon that in the readers; taking them to a separate word avoids the need to grab mount_lock on the write side. propagate_one(): get rid of dest_master propagate_mnt(): get rid of globals Linus asked to get rid of fs/pnode.c globals; done. take freeing of emptied mnt_namespace to namespace_unlock() A couple of commits made simpler by "prevent mount hash conflicts" - Rewrite of propagate_umount() reparenting is guaranteed that there won't be more than one overmount now, no loop needed. don't have mounts pin their parents simpler logics for "is there something other than overmount?" Rough overview: Part 1: fixes 1) replace collect_mounts()/drop_collected_mounts() with safer variant 2) attach_recursive_mnt(): do not lock the covering tree when sliding something under it Part 2: getting rid of mount hash conflicts for good 3) attach_mnt(): expand in attach_recursive_mnt(), then lose the flag argument 4) get rid of mnt_set_mountpoint_beneath() 5) prevent mount hash conflicts Part 3: trivial cleanups and helpers: 6) copy_tree(): don't set ->mnt_mountpoint on the root of copy 7) constify mnt_has_parent() 8) pnode: lift peers() into pnode.h 9) new predicate: mount_is_ancestor() 10) constify is_local_mountpoint() 11) new predicate: anon_ns_root(mount) 12) dissolve_on_fput(): use anon_ns_root() 13) __attach_mnt(): lose the second argument ... and rename to make_visible() 14) don't set MNT_LOCKED on parentless mounts 15) clone_mnt(): simplify the propagation-related logics 16) do_umount(): simplify the "is it still mounted" checks Part 4: (somewhat of a side story) restore the machinery for long-term mounts from accumulated bitrot. 17) sanitize handling of long-term internal mounts Part 5: propagate_umount() rewrite (posted last cycle) 18) Rewrite of propagate_umount() Part 6: untangling do_move_mount()/attach_recursive_mnt(). 19) make commit_tree() usable in same-namespace move case 20) attach_recursive_mnt(): unify the mnt_change_mountpoint() logics 21) attach_recursive_mnt(): pass destination mount in all cases 22) attach_recursive_mnt(): get rid of flags entirely 23) do_move_mount(): take dropping the old mountpoint into attach_recursive_mnt() 24) do_move_mount(): get rid of 'attached' flag Part 7: change locking for expiry lists. 25) attach_recursive_mnt(): remove from expiry list on move 26) take ->mnt_expire handling under mount_lock [read_seqlock_excl] Part 8: struct mountpoint massage. 27) pivot_root(): reorder tree surgeries, collapse unhash_mnt() and put_mountpoint() 28) combine __put_mountpoint() with unhash_mnt() 29) get rid of mountpoint->m_count Part 9: regularize mount refcounting a bit 30) don't have mounts pin their parents Part 10: misc stuff, will grow... 31) copy_tree(): don't link the mounts via mnt_list 32) mount: separate the flags accessed only under namespace_sem 33) propagate_one(): get rid of dest_master 34) propagate_mnt(): get rid of globals 35) take freeing of emptied mnt_namespace to namespace_unlock() Diffstat: Documentation/filesystems/porting.rst | 9 + Documentation/filesystems/propagate_umount.txt | 484 +++++++++++++++ drivers/gpu/drm/i915/gem/i915_gemfs.c | 21 +- drivers/gpu/drm/v3d/v3d_gemfs.c | 21 +- fs/hugetlbfs/inode.c | 2 +- fs/mount.h | 36 +- fs/namespace.c | 783 +++++++++++-------------- fs/pnode.c | 499 ++++++++-------- fs/pnode.h | 28 +- include/linux/mount.h | 24 +- ipc/mqueue.c | 2 +- kernel/audit_tree.c | 63 +- 12 files changed, 1214 insertions(+), 758 deletions(-) create mode 100644 Documentation/filesystems/propagate_umount.txt
