From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Kacur Subject: [PATCH 6/6] hvc_console: Fix race between hvc_close and hvc_remove Date: Tue, 15 Jun 2010 00:21:27 +0200 Message-ID: <1276554087-3632-7-git-send-email-jkacur@redhat.com> References: <1276554087-3632-1-git-send-email-jkacur@redhat.com> Cc: lkml , rt-users , Clark Williams , Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar To: Thomas Gleixner Return-path: Received: from mail-fx0-f46.google.com ([209.85.161.46]:55901 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757079Ab0FNWVm (ORCPT ); Mon, 14 Jun 2010 18:21:42 -0400 In-Reply-To: <1276554087-3632-1-git-send-email-jkacur@redhat.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: From: Anton Blanchard I don't claim to understand the tty layer, but it seems like hvc_open and hvc_close should be balanced in their kref reference counting. Right now we get a kref every call to hvc_open: if (hp->count++ > 0) { tty_kref_get(tty); <----- here spin_unlock_irqrestore(&hp->lock, flags); hvc_kick(); return 0; } /* else count == 0 */ tty->driver_data = hp; hp->tty = tty_kref_get(tty); <------ or here if hp->count was 0 But hvc_close has: tty_kref_get(tty); if (--hp->count == 0) { ... /* Put the ref obtained in hvc_open() */ tty_kref_put(tty); ... } tty_kref_put(tty); Since the outside kref get/put balance we only do a single kref_put when count reaches 0. The patch below changes things to call tty_kref_put once for every hvc_close call, and with that my machine boots fine. Signed-off-by: Anton Blanchard Acked-by: Amit Shah Signed-off-by: Rusty Russell Upstream-commit: 320718ee074acce5ffced6506cb51af1388942aa Signed-off-by: John Kacur --- drivers/char/hvc_console.c | 4 ---- 1 files changed, 0 insertions(+), 4 deletions(-) diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index da70f68..2898084 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -367,16 +367,12 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) hp = tty->driver_data; spin_lock_irqsave(&hp->lock, flags); - tty_kref_get(tty); if (--hp->count == 0) { /* We are done with the tty pointer now. */ hp->tty = NULL; spin_unlock_irqrestore(&hp->lock, flags); - /* Put the ref obtained in hvc_open() */ - tty_kref_put(tty);