Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935382Ab0BZLr6 (ORCPT ); Fri, 26 Feb 2010 06:47:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:15822 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935178Ab0BZLr4 (ORCPT ); Fri, 26 Feb 2010 06:47:56 -0500 From: Amit Shah To: linux-kernel@vger.kernel.org Cc: Amit Shah , Alan Cox , linuxppc-dev@ozlabs.org, Rusty Russell Subject: [PATCH] hvc_console: Fix a race between hvc_close and hvc_remove Date: Fri, 26 Feb 2010 17:16:26 +0530 Message-Id: <1267184786-4377-1-git-send-email-amit.shah@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2757 Lines: 92 Alan pointed out a race in the code where hvc_remove is invoked. The recent virtio_console work is the first user of hvc_remove(). Alan describes it thus: The hvc_console assumes that a close and remove call can't occur at the same time. In addition tty_hangup(tty) is problematic as tty_hangup is asynchronous itself.... So this can happen hvc_close hvc_remove hung up ? - no lock tty = hp->tty unlock lock hp->tty = NULL unlock notify del kref_put the hvc struct close completes tty is destroyed tty_hangup dead tty tty->ops will be NULL NULL->... This patch adds some tty krefs and also converts to using tty_vhangup() before putting the tty kref. Reported-by: Alan Cox Signed-off-by: Amit Shah CC: Alan Cox CC: linuxppc-dev@ozlabs.org CC: Rusty Russell --- I can't be sure if this is all that's needed. tty people, please take a look! drivers/char/hvc_console.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-) diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index d8dac58..3983e32 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -106,6 +106,7 @@ static struct hvc_struct *hvc_get_by_index(int index) spin_lock_irqsave(&hp->lock, flags); if (hp->index == index) { kref_get(&hp->kref); + tty_kref_get(hp->tty); spin_unlock_irqrestore(&hp->lock, flags); spin_unlock(&hvc_structs_lock); return hp; @@ -390,6 +391,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) } kref_put(&hp->kref, destroy_hvc_struct); + tty_kref_put(tty); } static void hvc_hangup(struct tty_struct *tty) @@ -806,6 +808,7 @@ int hvc_remove(struct hvc_struct *hp) unsigned long flags; struct tty_struct *tty; + tty_kref_get(hp->tty); spin_lock_irqsave(&hp->lock, flags); tty = hp->tty; @@ -830,7 +833,9 @@ int hvc_remove(struct hvc_struct *hp) * cleaned up the hvc_struct. */ if (tty) - tty_hangup(tty); + tty_vhangup(tty); + + tty_kref_put(hp->tty); return 0; } EXPORT_SYMBOL_GPL(hvc_remove); -- 1.6.2.5 -- 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/