linux-kernel - Re: [PATCH] xen: fix frontend driver disconnected from xenbus on removal

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Date:   Thu, 1 Feb 2018 22:24:47 +0200
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     jgross@...e.com, david.vrabel@...rix.com, otubo@...hat.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH] xen: fix frontend driver disconnected from xenbus on
 removal



On 02/01/2018 10:08 PM, Boris Ostrovsky wrote:
> On 02/01/2018 03:57 AM, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
>>
>> Current xenbus frontend driver removal flow first disconnects
>> the driver from xenbus and then calls driver's remove callback.
>> This makes it impossible for the driver to listen to backend's
>> state changes and synchronize the removal procedure.
>>
>> Fix this by removing other end XenBus watches after the
>> driver's remove callback is called.
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
>> ---
>>   drivers/xen/xenbus/xenbus_probe.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
>> index 74888cacd0b0..9c63cd3f416b 100644
>> --- a/drivers/xen/xenbus/xenbus_probe.c
>> +++ b/drivers/xen/xenbus/xenbus_probe.c
>> @@ -258,11 +258,11 @@ int xenbus_dev_remove(struct device *_dev)
>>   
>>   	DPRINTK("%s", dev->nodename);
>>   
>> -	free_otherend_watch(dev);
>> -
>>   	if (drv->remove)
>>   		drv->remove(dev);
>
> Is it possible for the watch to fire here?
Indeed. Yes, It is possible, so we have to somehow protect the removed
driver from being called, e.g. the driver cleans up in its .remove,
but watch may still trigger .otherend_changed callback.
Is this what you mean?
If so, do you have something neat on your mind how to solve this?
> -boris
>
>>   
>> +	free_otherend_watch(dev);
>> +
>>   	free_otherend_details(dev);
>>   
>>   	xenbus_switch_state(dev, XenbusStateClosed);
Thank you,
Oleksandr