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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
View file

@ -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;
}

26
drivers/lguest/interrupts_and_traps.c
View file

@ -128,30 +128,38 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
/*H:205
* Virtual Interrupts.
*
* maybe_do_interrupt() gets called before every entry to the Guest, to see if
* we should divert the Guest to running an interrupt handler. */
void maybe_do_interrupt(struct lg_cpu *cpu)
* interrupt_pending() returns the first pending interrupt which isn't blocked
* by the Guest. It is called before every entry to the Guest, and just before
* we go to sleep when the Guest has halted itself. */
unsigned int interrupt_pending(struct lg_cpu *cpu)
{
unsigned int irq;
DECLARE_BITMAP(blk, LGUEST_IRQS);
struct desc_struct *idt;
/* If the Guest hasn't even initialized yet, we can do nothing. */
if (!cpu->lg->lguest_data)
return;
return LGUEST_IRQS;
/* Take our "irqs_pending" array and remove any interrupts the Guest
* wants blocked: the result ends up in "blk". */
if (copy_from_user(&blk, cpu->lg->lguest_data->blocked_interrupts,
sizeof(blk)))
return;
return LGUEST_IRQS;
bitmap_andnot(blk, cpu->irqs_pending, blk, LGUEST_IRQS);
/* Find the first interrupt. */
irq = find_first_bit(blk, LGUEST_IRQS);
/* None? Nothing to do */
if (irq >= LGUEST_IRQS)
return;
return irq;
}
/* This actually diverts the Guest to running an interrupt handler, once an
* interrupt has been identified by interrupt_pending(). */
void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq)
{
struct desc_struct *idt;
BUG_ON(irq >= LGUEST_IRQS);
/* They may be in the middle of an iret, where they asked us never to
* deliver interrupts. */

3
drivers/lguest/lg.h
View file

@ -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);