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lguest: fix race in halt code

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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>
This commit is contained in:
Rusty Russell
2009-06-12 22:27:02 -06:00
parent ebf9a5a99c
commit abd41f037e
3 changed files with 31 additions and 12 deletions
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14
drivers/lguest/core.c
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@@ -188,6 +188,8 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
{
/* 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 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
/* 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 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
* 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;
}