lguest: fix race in halt code
When the Guest does the LHCALL_HALT hypercall, we go to sleep, expecting
that a timer or the Waker will wake_up_process() us.
But we do it in a stupid way, leaving a classic missing wakeup race.
So split maybe_do_interrupt() into interrupt_pending() and
try_deliver_interrupt(), and check maybe_do_interrupt() and the
"break_out" flag before calling schedule.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 4845fb3..8ca1def 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -188,6 +188,8 @@
{
/* We stop running once the Guest is dead. */
while (!cpu->lg->dead) {
+ unsigned int irq;
+
/* First we run any hypercalls the Guest wants done. */
if (cpu->hcall)
do_hypercalls(cpu);
@@ -211,7 +213,9 @@
/* Check if there are any interrupts which can be delivered now:
* if so, this sets up the hander to be executed when we next
* run the Guest. */
- maybe_do_interrupt(cpu);
+ irq = interrupt_pending(cpu);
+ if (irq < LGUEST_IRQS)
+ try_deliver_interrupt(cpu, irq);
/* All long-lived kernel loops need to check with this horrible
* thing called the freezer. If the Host is trying to suspend,
@@ -227,7 +231,13 @@
* clock timer or LHREQ_BREAK from the Waker will wake us. */
if (cpu->halted) {
set_current_state(TASK_INTERRUPTIBLE);
- schedule();
+ /* Just before we sleep, make sure nothing snuck in
+ * which we should be doing. */
+ if (interrupt_pending(cpu) < LGUEST_IRQS
+ || cpu->break_out)
+ set_current_state(TASK_RUNNING);
+ else
+ schedule();
continue;
}