Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965873Ab2ERLFf (ORCPT ); Fri, 18 May 2012 07:05:35 -0400 Received: from mail-yw0-f46.google.com ([209.85.213.46]:60817 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752718Ab2ERLFe (ORCPT ); Fri, 18 May 2012 07:05:34 -0400 MIME-Version: 1.0 From: Rabin Vincent Date: Fri, 18 May 2012 16:34:53 +0530 X-Google-Sender-Auth: QaD_ZTn2OkvOKTaenNM5VyWlAyw Message-ID: Subject: Race in vt_event_wait() during suspend/resume To: alan@linux.intel.com, gregkh@linuxfoundation.org Cc: LKML Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3053 Lines: 109 pm_restore_console() is called from the suspend/resume path, this calls vt_move_to_console(), which calls vt_event_wait(). 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 I think the following should fix it. Comments? diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c index ede2ef1..1d02e32 100644 --- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -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 */ @@ -129,8 +120,18 @@ 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); @@ -138,6 +139,22 @@ static void vt_event_wait(struct vt_event_wait *vw) } /** + * 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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/