Re: Freezer: Don't count threads waiting for frozen filesystems.

[Pavel Machek <pavel@ucw.cz>]

Hi!

> While working on freezing fuse filesystems, I found that if a filesystem
> is frozen when we try to freeze processes, freezing can fail because
> threads are waiting in vfs_check_frozen for the filesystem to be thawed.
> We should thus not count such threads.
> 
> The check will be safe if a filesystem is thawed while we're freezing
> processes because filesystem thaws are only invoked from userspace. Any
> waiting processes will be woken and frozen prior to us completing the
> freezing of userspace (the caller invoking the filesystem thaw will be
> freezing) or - in the worst case - together with kernel threads.

In the worst case we have a problem.

Userspace and kernel threads *need* to be frozen separately...

(Otherwise its a race, and if you freeze kjournald first, user process
becomes unfreezeable and freezing fails.)
									Pavel

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