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SubjectRe: [PATCH] xen-netfront: remove warning when unloading module
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On 20/11/17 11:49, Wei Liu wrote:
> CC netfront maintainers.
>
> On Mon, Nov 20, 2017 at 11:41:09AM +0100, Eduardo Otubo wrote:
>> When unloading module xen_netfront from guest, dmesg would output
>> warning messages like below:
>>
>> [ 105.236836] xen:grant_table: WARNING: g.e. 0x903 still in use!
>> [ 105.236839] deferring g.e. 0x903 (pfn 0x35805)
>>
>> This problem relies on netfront and netback being out of sync. By the time
>> netfront revokes the g.e.'s netback didn't have enough time to free all of
>> them, hence displaying the warnings on dmesg.
>>
>> The trick here is to make netfront to wait until netback frees all the g.e.'s
>> and only then continue to cleanup for the module removal, and this is done by
>> manipulating both device states.
>>
>> Signed-off-by: Eduardo Otubo <otubo@redhat.com>
>> ---
>> drivers/net/xen-netfront.c | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>> index 8b8689c6d887..b948e2a1ce40 100644
>> --- a/drivers/net/xen-netfront.c
>> +++ b/drivers/net/xen-netfront.c
>> @@ -2130,6 +2130,17 @@ static int xennet_remove(struct xenbus_device *dev)
>>
>> dev_dbg(&dev->dev, "%s\n", dev->nodename);
>>
>> + xenbus_switch_state(dev, XenbusStateClosing);
>> + while (xenbus_read_driver_state(dev->otherend) != XenbusStateClosing){
>> + cpu_relax();
>> + schedule();
>> + }
>> + xenbus_switch_state(dev, XenbusStateClosed);
>> + while (dev->xenbus_state != XenbusStateClosed){
>> + cpu_relax();
>> + schedule();
>> + }

I really don't like the busy waits.

Can't you use e.g. a wait queue and wait_event_interruptible() instead?

BTW: what happens if the device is already in closed state if you enter
xennet_remove()? In case this is impossible, please add a comment to
indicate you've thought about that case.

Other than that: you should run ./scripts/checkpatch.p1 against your
patch to avoid common style problems.


Juergen

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