Commit a7b12929 authored by Rabin Vincent's avatar Rabin Vincent Committed by Greg Kroah-Hartman
Browse files

vt: fix race in vt_waitactive() 



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: default avatarRabin Vincent <rabin.vincent@stericsson.com>
Acked-by: default avatarAlan Cox <alan@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ed85c604

drivers/tty/vt/vt_ioctl.c

+34 −13
Original line number Diff line number Diff line
@@ -110,16 +110,7 @@ void vt_event_post(unsigned int event, unsigned int old, unsigned int new) 
		wake_up_interruptible(&vt_event_waitqueue);

}



/**

 *	vt_event_wait		-	wait for an event

 *	@vw: our event

 *

 *	Waits for an event to occur which completes our vt_event_wait

 *	structure. On return the structure has wv->done set to 1 for success

 *	or 0 if some event such as a signal ended the wait.

 */



static void vt_event_wait(struct vt_event_wait *vw)

static void __vt_event_queue(struct vt_event_wait *vw)

{

	unsigned long flags;

	/* Prepare the event */
@@ -129,14 +120,40 @@ static void vt_event_wait(struct vt_event_wait *vw) 
	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

 *

 *	Waits for an event to occur which completes our vt_event_wait

 *	structure. On return the structure has wv->done set to 1 for success

 *	or 0 if some event such as a signal ended the wait.

 */



static void vt_event_wait(struct vt_event_wait *vw)

{

	__vt_event_queue(vw);

	__vt_event_wait(vw);

	__vt_event_dequeue(vw);

}



/**

 *	vt_event_wait_ioctl	-	event ioctl handler

 *	@arg: argument to ioctl
@@ -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);

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