Crap, ksoftirqd/0 looping forever in softirq

[Paul Gortmaker <paul.gortmaker@windriver.com>]

Seeing the above message, I added a trivial change to print out the
Mask and Pending, and I consistently saw it was (both p/m) in every
case `was __IRQF_TIMER (0x200).

Looking at do_current_softirqs, it seems that it implicitly expects
two entrance paths:

   /*
    * Called with interrupts disabled. Process softirqs which were raised
    * in current context (or on behalf of ksoftirqd).
    */
   static void do_current_softirqs(int need_rcu_bh_qs)

In there, we loop on current->softirqs_raised, but there is no "filter"
for the case where we spawn from ksoftirqd with __IRQF_TIMER, or more
specifically IRQF_NO_THREAD.  Asking ksoftirqd to handle IRQF_NO_THREAD?

So based on my dain-bramaged and limited understanding, it seems that
we are waiting on completion from ksoftirqd on something that we've
asked to be not run from a thread.  I'd propose a patch but I'd probably
only manage to hurt myself, so I'll stop at reporting the above data,
and leave it to the folks more in the know to suggest a proper fix...

Paul.