netdev - Re: [PATCH 2/2] xen-netback: cancel the credit timer when taking the vif down

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Message-ID: <1360859947.20449.465.camel@zakaz.uk.xensource.com>
Date:	Thu, 14 Feb 2013 16:39:07 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	"Christopher S. Aker" <caker@...shore.net>
CC:	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Jan Beulich <jbeulich@...e.com>,
	"Wei Liu (3P)" <wei.liu@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/2] xen-netback: cancel the credit timer when taking
 the vif down

On Thu, 2013-02-14 at 13:18 +0000, David Vrabel wrote:
> From: David Vrabel <david.vrabel@...rix.com>
> 
> If the credit timer is left armed after calling
> xen_netbk_remove_xenvif(), then it may fire and attempt to schedule
> the vif which will then oops as vif->netbk == NULL.
> 
> This may happen both in the fatal error path and during normal
> disconnection from the front end.
> 
> The sequencing during shutdown is critical to ensure that: a)
> vif->netbk doesn't become unexpectedly NULL; and b) the net device/vif
> is not freed.
> 
> 1. Mark as unschedulable (netif_carrier_off()).
> 2. Synchronously cancel the timer.
> 3. Remove the vif from the schedule list.
> 4. Remove it from it netback thread group.
> 5. Wait for vif->refcnt to become 0.
> 
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>

Acked-by: Ian Campbell <ian.campbell@...rix.com>

Was this one also Reported-by Christopher S. Aker or was it just
discovered in the process of investigating?

Another stable candidate please Dave.

> ---
>  drivers/net/xen-netback/interface.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index b8c5193..221f426 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -132,6 +132,7 @@ static void xenvif_up(struct xenvif *vif)
>  static void xenvif_down(struct xenvif *vif)
>  {
>  	disable_irq(vif->irq);
> +	del_timer_sync(&vif->credit_timeout);
>  	xen_netbk_deschedule_xenvif(vif);
>  	xen_netbk_remove_xenvif(vif);
>  }
> @@ -363,8 +364,6 @@ void xenvif_disconnect(struct xenvif *vif)
>  	atomic_dec(&vif->refcnt);
>  	wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
>  
> -	del_timer_sync(&vif->credit_timeout);
> -
>  	if (vif->irq)
>  		unbind_from_irqhandler(vif->irq, vif);
>  


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