[linux-pm] Freezer: Don't count threads waiting for frozen filesystems.
Miklos Szeredi
miklos at szeredi.hu
Fri Oct 31 01:49:06 PDT 2008
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
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