From abd41f037e1a64543000ed73b42f616d04d92700 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Fri, 12 Jun 2009 22:27:02 -0600 Subject: 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 --- drivers/lguest/core.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'drivers/lguest/core.c') diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c index 4845fb3cf74b..8ca1def5b142 100644 --- a/drivers/lguest/core.c +++ b/drivers/lguest/core.c @@ -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; } -- cgit v1.2.3