Messages in this thread | | | Date | Thu, 2 Aug 2018 22:29:23 +0100 | From | Al Viro <> | Subject | Re: [PATCH 01/33] vfs: syscall: Add open_tree(2) to reference or clone a mount [ver #11] |
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On Thu, Aug 02, 2018 at 06:31:06PM +0100, Alan Jenkins wrote: > Hi > > I found this interesting, though I don't entirely follow the kernel > mount/unmount code. I had one puzzle about the code, and two questions > which I was largely able to answer. > > On 01/08/18 16:24, David Howells wrote: > > +void dissolve_on_fput(struct vfsmount *mnt) > > +{ > > + namespace_lock(); > > + lock_mount_hash(); > > + mntget(mnt); > > + umount_tree(real_mount(mnt), UMOUNT_SYNC); > > + unlock_mount_hash(); > > + namespace_unlock(); > > +} > > Can I ask why UMOUNT_SYNC is used here? I feel like I must have missed > something, but doesn't it skip the IS_MNT_LOCKED() check in > disconnect_mount() ? > > UMOUNT_SYNC seems used for non-lazy unmounts, and in internal cleanups where > userspace wouldn't be able to see. But I think userspace can keep watching > in this case, e.g. by `fd2 = openat(fd, ".", O_PATH)` (or `fd2 = > open_tree(fd, ".", 0)` ?). I would think this function should avoid using > UMOUNT_SYNC, like lazy unmount avoids it.
FWIW, I suspect that UMOUNT_CONNECTED might be the right thing here...
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