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

From: David Vrabel <[email-masked]>
Date: Thu, 14 Feb 2013 13:56:24 +0000

On 14/02/13 13:53, Wei Liu wrote:
> On Thu, 2013-02-14 at 13:18 +0000, David Vrabel wrote:
>> From: David Vrabel <[email-masked]>
>>
>> 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 <[email-masked]>
> 
> You would need to reinitialize the timer in xenvif_up, given that user
> might `ifconfig vifX.X down; ifconfig vifX.X up`.

No.  Deleted timers do not need to be reinitialized.  The timer will be
armed as usual with mod_timer() when credit is next exhausted.

David