illumos gate

During development of the emlxs driver Bob Warning of ATTO found that hardware interrupts could go missing. He analyzed that issue and found a bug in apix. Here's what happens:

• a softint is running at IPL x
• hardint a comes in at IPL x and is put on the pending queue, bit x being set in x_intr_pending
• softint finishes, and the harding stays pending
• time passes
• hardint b comes in at IPL x, clears bit x in x_intr_pending (in apix_intr_thread_prolog())
• hardint b finishes, but apix_do_pending_hardint() doesn't see pending hardint a as bit x isn't set in x_intr_pending

Bob was also able to reproduce this with a QLogic FC card.

The fix is actually pretty simple: After finishing the softint processing, check the queues for newly added interrupts again and process them immediately.