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vt: fix race in vt_waitactive()

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pm_restore_console() is called from the suspend/resume path, and this
calls vt_move_to_console(), which calls vt_waitactive().

There's a race in this path which causes the process which requests the
suspend to sleep indefinitely waiting for an event which already
happened:

P1                                      P2
 vt_move_to_console()
  set_console()
    schedule_console_callback()
  vt_waitactive()
    check n == fg_console +1
                                       console_callback()
                                         switch_screen()
                                         vt_event_post() // no waiters

    vt_event_wait() // forever

Fix the race by ensuring we're registered for the event before we check
if it's already completed.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Rabin Vincent 2012-05-21 13:38:42 +05:30 committed by Greg Kroah-Hartman
parent ed85c60457
commit a7b12929be
1 changed files with 38 additions and 17 deletions
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55
drivers/tty/vt/vt_ioctl.c
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@ -110,6 +110,34 @@ void vt_event_post(unsigned int event, unsigned int old, unsigned int new)
wake_up_interruptible(&vt_event_waitqueue);
}
static void __vt_event_queue(struct vt_event_wait *vw)
{
unsigned long flags;
/* Prepare the event */
INIT_LIST_HEAD(&vw->list);
vw->done = 0;
/* Queue our event */
spin_lock_irqsave(&vt_event_lock, flags);
list_add(&vw->list, &vt_events);
spin_unlock_irqrestore(&vt_event_lock, flags);
}
static void __vt_event_wait(struct vt_event_wait *vw)
{
/* Wait for it to pass */
wait_event_interruptible(vt_event_waitqueue, vw->done);
}
static void __vt_event_dequeue(struct vt_event_wait *vw)
{
unsigned long flags;
/* Dequeue it */
spin_lock_irqsave(&vt_event_lock, flags);
list_del(&vw->list);
spin_unlock_irqrestore(&vt_event_lock, flags);
}
/**
* vt_event_wait - wait for an event
* @vw: our event
@ -121,20 +149,9 @@ void vt_event_post(unsigned int event, unsigned int old, unsigned int new)
static void vt_event_wait(struct vt_event_wait *vw)
{
unsigned long flags;
/* Prepare the event */
INIT_LIST_HEAD(&vw->list);
vw->done = 0;
/* Queue our event */
spin_lock_irqsave(&vt_event_lock, flags);
list_add(&vw->list, &vt_events);
spin_unlock_irqrestore(&vt_event_lock, flags);
/* Wait for it to pass */
wait_event_interruptible(vt_event_waitqueue, vw->done);
/* Dequeue it */
spin_lock_irqsave(&vt_event_lock, flags);
list_del(&vw->list);
spin_unlock_irqrestore(&vt_event_lock, flags);
__vt_event_queue(vw);
__vt_event_wait(vw);
__vt_event_dequeue(vw);
}
/**
@ -177,10 +194,14 @@ int vt_waitactive(int n)
{
struct vt_event_wait vw;
do {
if (n == fg_console + 1)
break;
vw.event.event = VT_EVENT_SWITCH;
vt_event_wait(&vw);
__vt_event_queue(&vw);
if (n == fg_console + 1) {
__vt_event_dequeue(&vw);
break;
}
__vt_event_wait(&vw);
__vt_event_dequeue(&vw);
if (vw.done == 0)
return -EINTR;
} while (vw.event.newev != n);