A new instance of user mode linux that I created over the past couple of
days worked pretty well except that it had a habit of freezing after a
few minutes. Every time it froze, the last message on the console was
spurious interrupt in ubd_handler, err = 4
spurious interrupt in ubd_handler, err = 0
This message is generated by arch/um/drivers/ubd_kern.c. I did not work
out the cause of the spurious interrupts, but I did come up with a patch
that makes the guest recover from spurious interrupts without freezing.
It appears that the interrupt handler needs to be reactivated before
every exit of ubd_handler(). The patch is below.
@@ -489,6 +489,7 @@
printk(KERN_ERR "spurious interrupt in
"err = %d\n", -n);
+ reactivate_fd(thread_fd, UBD_IRQ);