Re: [linux-pm] Freezer: Don't count threads waiting for frozen filesystems.

[Miklos Szeredi <miklos@szeredi.hu>]

On Fri, 31 Oct 2008, Nigel Cunningham wrote:
> I'm not sure that's true. You see, I'm thinking of this as not that
> different to the problem of unmounting filesystems. There, too, we need
> to unmount in a particular order, and let transactions on each
> filesystem stop cleanly before we can unmount them. Even if there are
> differences, perhaps looking at how we handle unmounting will help with
> handling freezing.

There's nothing magic about umount, it just uses a refcount on the fs.

But umount changes the namespace, that's the big difference.  For
example if a process is accessing path P which has a component inside
the mount, it _will_ get different results before and after the
umount.  This is not acceptable for freezing.

For freezing to work with such a refcounting scheme, we'd have to
count _future_ uses of the fs as well, not just current ones, which is
obviously impossible.

Miklos