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>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index af92a176697..6743cf147d9 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -139,7 +139,8 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user);
 #define pgd_pfn(x)      (pgd_val(x) >> PAGE_SHIFT)
 
 /* interrupts_and_traps.c: */
-void maybe_do_interrupt(struct lg_cpu *cpu);
+unsigned int interrupt_pending(struct lg_cpu *cpu);
+void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq);
 bool deliver_trap(struct lg_cpu *cpu, unsigned int num);
 void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int i,
                           u32 low, u32 hi);