[Devel] Re: [PATCH] usbatm: Update to use the kthread api.

[Duncan Sands]

On Friday 15 December 2006 11:45, Eric W. Biederman wrote:
> Christoph Hellwig <hch at infradead.org> writes:
> 
> > On Fri, Dec 15, 2006 at 03:17:57AM -0700, Eric W. Biederman wrote:
> >
> > I think the right fix is to encehance the kthread infrastructure to
> > gracefully handle the case where the threat has stopped by itself
> > and doesn't exist anymore at the time where we call kthread_stop.
> 
> Yep that is about where I thought we were at.  Now we need to figure out
> how to do that cleanly, and sanely.

There's a completely different solution, which is to use a workqueue
instead of a kthread, with users providing a cancellation method.
Recall that the functionality is provided by usbatm to drivers:
they use it to perform slow initialization that is too slow to be
done in the probe method.  They register with usbatm, providing a
"heavy_init" method.  They could also provide a "heavy_cancel" method.
(Any special data that heavy_cancel needs can be stored in the
existing driver private data structure; this structure is already
passed to heavy_init).  In the case of the speedtch driver, it
could place a completion in its private data structure; heavy_cancel
would just complete the completion.  Rather than doing interruptible
sleeps, it can use wait_for_completion_timeout.

The only thing that worries me about this solution is... that you
can't shoot down firmware loading from userspace anymore.  For
example, if heavy_init is blocked loading firmware when the system
is halted, it presumably won't react to the kill signal.  Perhaps
it is unimportant; and if not, I guess I can just re-enable signals
in heavy_init.

Ciao,

Duncan.
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