fs/namespace: notify pollers of legacy propagation changes

Changing mount propagation through the legacy mount API changes
user-visible mountinfo contents, including the shared: and master:
optional fields.

The mount_setattr() path already touches the mount namespace after
change_mnt_propagation(), so pollers of /proc/<pid>/mountinfo are woken
when the namespace event changes.

The legacy mount --make-* path also changes propagation through
change_mnt_propagation(), and MOVE_MOUNT_SET_GROUP updates the
propagation relationship of the target mount. Both paths currently
return without touching the affected mount namespace.

As a result, userspace polling /proc/<pid>/mountinfo can miss these
propagation-only changes even though mountinfo has changed.

A simple reproducer that polls /proc/self/mountinfo while changing
propagation shows the inconsistency.

Before this change:

  legacy MS_SHARED: poll ret=0 revents=0x0
  mount_setattr MS_SHARED: poll ret=1 revents=0xa

After this change:

  legacy MS_SHARED: poll ret=1 revents=0xa
  mount_setattr MS_SHARED: poll ret=1 revents=0xa

Fix this by touching the affected mount namespace after successful
propagation changes in do_change_type() and do_set_group().

Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Link: https://patch.msgid.link/20260601032911.940507-1-guopeng.zhang@linux.dev
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions