From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755585Ab0CXKrL (ORCPT ); Wed, 24 Mar 2010 06:47:11 -0400 Received: from gate.crashing.org ([63.228.1.57]:40679 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755363Ab0CXKrJ (ORCPT ); Wed, 24 Mar 2010 06:47:09 -0400 Subject: Re: [PATCH 4/7] hvc_console: Fix race between hvc_close and hvc_remove From: Benjamin Herrenschmidt To: Linus Torvalds Cc: Greg KH , linux-kernel@vger.kernel.org, Amit Shah , linuxppc-dev@ozlabs.org, Rusty Russell , Alan Cox In-Reply-To: <1269119079.8599.65.camel@pasglop> References: <20100319151326.GC8541@kroah.com> <1269011916-8836-4-git-send-email-gregkh@suse.de> <1269119079.8599.65.camel@pasglop> Content-Type: text/plain; charset="UTF-8" Date: Wed, 24 Mar 2010 21:45:44 +1100 Message-ID: <1269427544.8599.222.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2010-03-21 at 08:04 +1100, Benjamin Herrenschmidt wrote: > On Fri, 2010-03-19 at 08:18 -0700, Greg Kroah-Hartman wrote: > > From: Amit Shah > > > > 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(). > > This causes hangs during boot on pseries machines. Haven't had a chance > to track that down yet, but please revert > e74d098c66543d0731de62eb747ccd5b636a6f4c for now. Linus, any chance you can revert that one for now until we figure out what's wrong ? Thanks ! Cheers, Ben. > Cheers, > Ben. > > > > 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(). > > > > Reported-by: Alan Cox > > Signed-off-by: Amit Shah > > CC: Alan Cox > > CC: linuxppc-dev@ozlabs.org > > CC: Rusty Russell > > Signed-off-by: Greg Kroah-Hartman > > --- > > drivers/char/hvc_console.c | 31 +++++++++++++++++++++---------- > > 1 files changed, 21 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c > > index 465185f..ba55bba 100644 > > --- a/drivers/char/hvc_console.c > > +++ b/drivers/char/hvc_console.c > > @@ -312,6 +312,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) > > spin_lock_irqsave(&hp->lock, flags); > > /* Check and then increment for fast path open. */ > > if (hp->count++ > 0) { > > + tty_kref_get(tty); > > spin_unlock_irqrestore(&hp->lock, flags); > > hvc_kick(); > > return 0; > > @@ -319,7 +320,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) > > > > tty->driver_data = hp; > > > > - hp->tty = tty; > > + hp->tty = tty_kref_get(tty); > > > > spin_unlock_irqrestore(&hp->lock, flags); > > > > @@ -336,6 +337,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) > > spin_lock_irqsave(&hp->lock, flags); > > hp->tty = NULL; > > spin_unlock_irqrestore(&hp->lock, flags); > > + tty_kref_put(tty); > > tty->driver_data = NULL; > > kref_put(&hp->kref, destroy_hvc_struct); > > printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc); > > @@ -363,13 +365,18 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) > > return; > > > > 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); > > + > > if (hp->ops->notifier_del) > > hp->ops->notifier_del(hp, hp->data); > > > > @@ -389,6 +396,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) > > spin_unlock_irqrestore(&hp->lock, flags); > > } > > > > + tty_kref_put(tty); > > kref_put(&hp->kref, destroy_hvc_struct); > > } > > > > @@ -424,10 +432,11 @@ static void hvc_hangup(struct tty_struct *tty) > > spin_unlock_irqrestore(&hp->lock, flags); > > > > if (hp->ops->notifier_hangup) > > - hp->ops->notifier_hangup(hp, hp->data); > > + hp->ops->notifier_hangup(hp, hp->data); > > > > while(temp_open_count) { > > --temp_open_count; > > + tty_kref_put(tty); > > kref_put(&hp->kref, destroy_hvc_struct); > > } > > } > > @@ -592,7 +601,7 @@ int hvc_poll(struct hvc_struct *hp) > > } > > > > /* No tty attached, just skip */ > > - tty = hp->tty; > > + tty = tty_kref_get(hp->tty); > > if (tty == NULL) > > goto bail; > > > > @@ -672,6 +681,8 @@ int hvc_poll(struct hvc_struct *hp) > > > > tty_flip_buffer_push(tty); > > } > > + if (tty) > > + tty_kref_put(tty); > > > > return poll_mask; > > } > > @@ -807,7 +818,7 @@ int hvc_remove(struct hvc_struct *hp) > > struct tty_struct *tty; > > > > spin_lock_irqsave(&hp->lock, flags); > > - tty = hp->tty; > > + tty = tty_kref_get(hp->tty); > > > > if (hp->index < MAX_NR_HVC_CONSOLES) > > vtermnos[hp->index] = -1; > > @@ -819,18 +830,18 @@ int hvc_remove(struct hvc_struct *hp) > > /* > > * We 'put' the instance that was grabbed when the kref instance > > * was initialized using kref_init(). Let the last holder of this > > - * kref cause it to be removed, which will probably be the tty_hangup > > + * kref cause it to be removed, which will probably be the tty_vhangup > > * below. > > */ > > kref_put(&hp->kref, destroy_hvc_struct); > > > > /* > > - * This function call will auto chain call hvc_hangup. The tty should > > - * always be valid at this time unless a simultaneous tty close already > > - * cleaned up the hvc_struct. > > + * This function call will auto chain call hvc_hangup. > > */ > > - if (tty) > > - tty_hangup(tty); > > + if (tty) { > > + tty_vhangup(tty); > > + tty_kref_put(tty); > > + } > > return 0; > > } > > EXPORT_SYMBOL_GPL(hvc_remove); > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 90513B7CF9 for ; Wed, 24 Mar 2010 21:46:52 +1100 (EST) Subject: Re: [PATCH 4/7] hvc_console: Fix race between hvc_close and hvc_remove From: Benjamin Herrenschmidt To: Linus Torvalds In-Reply-To: <1269119079.8599.65.camel@pasglop> References: <20100319151326.GC8541@kroah.com> <1269011916-8836-4-git-send-email-gregkh@suse.de> <1269119079.8599.65.camel@pasglop> Content-Type: text/plain; charset="UTF-8" Date: Wed, 24 Mar 2010 21:45:44 +1100 Message-ID: <1269427544.8599.222.camel@pasglop> Mime-Version: 1.0 Cc: Greg KH , Rusty Russell , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Amit Shah , Alan Cox List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, 2010-03-21 at 08:04 +1100, Benjamin Herrenschmidt wrote: > On Fri, 2010-03-19 at 08:18 -0700, Greg Kroah-Hartman wrote: > > From: Amit Shah > > > > 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(). > > This causes hangs during boot on pseries machines. Haven't had a chance > to track that down yet, but please revert > e74d098c66543d0731de62eb747ccd5b636a6f4c for now. Linus, any chance you can revert that one for now until we figure out what's wrong ? Thanks ! Cheers, Ben. > Cheers, > Ben. > > > > 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(). > > > > Reported-by: Alan Cox > > Signed-off-by: Amit Shah > > CC: Alan Cox > > CC: linuxppc-dev@ozlabs.org > > CC: Rusty Russell > > Signed-off-by: Greg Kroah-Hartman > > --- > > drivers/char/hvc_console.c | 31 +++++++++++++++++++++---------- > > 1 files changed, 21 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c > > index 465185f..ba55bba 100644 > > --- a/drivers/char/hvc_console.c > > +++ b/drivers/char/hvc_console.c > > @@ -312,6 +312,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) > > spin_lock_irqsave(&hp->lock, flags); > > /* Check and then increment for fast path open. */ > > if (hp->count++ > 0) { > > + tty_kref_get(tty); > > spin_unlock_irqrestore(&hp->lock, flags); > > hvc_kick(); > > return 0; > > @@ -319,7 +320,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) > > > > tty->driver_data = hp; > > > > - hp->tty = tty; > > + hp->tty = tty_kref_get(tty); > > > > spin_unlock_irqrestore(&hp->lock, flags); > > > > @@ -336,6 +337,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) > > spin_lock_irqsave(&hp->lock, flags); > > hp->tty = NULL; > > spin_unlock_irqrestore(&hp->lock, flags); > > + tty_kref_put(tty); > > tty->driver_data = NULL; > > kref_put(&hp->kref, destroy_hvc_struct); > > printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc); > > @@ -363,13 +365,18 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) > > return; > > > > 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); > > + > > if (hp->ops->notifier_del) > > hp->ops->notifier_del(hp, hp->data); > > > > @@ -389,6 +396,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) > > spin_unlock_irqrestore(&hp->lock, flags); > > } > > > > + tty_kref_put(tty); > > kref_put(&hp->kref, destroy_hvc_struct); > > } > > > > @@ -424,10 +432,11 @@ static void hvc_hangup(struct tty_struct *tty) > > spin_unlock_irqrestore(&hp->lock, flags); > > > > if (hp->ops->notifier_hangup) > > - hp->ops->notifier_hangup(hp, hp->data); > > + hp->ops->notifier_hangup(hp, hp->data); > > > > while(temp_open_count) { > > --temp_open_count; > > + tty_kref_put(tty); > > kref_put(&hp->kref, destroy_hvc_struct); > > } > > } > > @@ -592,7 +601,7 @@ int hvc_poll(struct hvc_struct *hp) > > } > > > > /* No tty attached, just skip */ > > - tty = hp->tty; > > + tty = tty_kref_get(hp->tty); > > if (tty == NULL) > > goto bail; > > > > @@ -672,6 +681,8 @@ int hvc_poll(struct hvc_struct *hp) > > > > tty_flip_buffer_push(tty); > > } > > + if (tty) > > + tty_kref_put(tty); > > > > return poll_mask; > > } > > @@ -807,7 +818,7 @@ int hvc_remove(struct hvc_struct *hp) > > struct tty_struct *tty; > > > > spin_lock_irqsave(&hp->lock, flags); > > - tty = hp->tty; > > + tty = tty_kref_get(hp->tty); > > > > if (hp->index < MAX_NR_HVC_CONSOLES) > > vtermnos[hp->index] = -1; > > @@ -819,18 +830,18 @@ int hvc_remove(struct hvc_struct *hp) > > /* > > * We 'put' the instance that was grabbed when the kref instance > > * was initialized using kref_init(). Let the last holder of this > > - * kref cause it to be removed, which will probably be the tty_hangup > > + * kref cause it to be removed, which will probably be the tty_vhangup > > * below. > > */ > > kref_put(&hp->kref, destroy_hvc_struct); > > > > /* > > - * This function call will auto chain call hvc_hangup. The tty should > > - * always be valid at this time unless a simultaneous tty close already > > - * cleaned up the hvc_struct. > > + * This function call will auto chain call hvc_hangup. > > */ > > - if (tty) > > - tty_hangup(tty); > > + if (tty) { > > + tty_vhangup(tty); > > + tty_kref_put(tty); > > + } > > return 0; > > } > > EXPORT_SYMBOL_GPL(hvc_remove); >