linux-kernel - Re: [PATCH v2] xen-netfront: Improve error handling during initialization

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Date:   Wed, 8 Feb 2017 10:32:59 +0000
From:   Ross Lagerwall <ross.lagerwall@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        <xen-devel@...ts.xenproject.org>
CC:     <netdev@...r.kernel.org>, Juergen Gross <jgross@...e.com>,
        <linux-kernel@...r.kernel.org>, <wei.liu2@...rix.com>
Subject: Re: [PATCH v2] xen-netfront: Improve error handling during
 initialization

On 02/07/2017 11:33 PM, Boris Ostrovsky wrote:
> On 02/07/2017 09:55 AM, Ross Lagerwall wrote:
>> This fixes a crash when running out of grant refs when creating many
>> queues across many netdevs.
>>
>> * If creating queues fails (i.e. there are no grant refs available),
>> call xenbus_dev_fatal() to ensure that the xenbus device is set to the
>> closed state.
>> * If no queues are created, don't call xennet_disconnect_backend as
>> netdev->real_num_tx_queues will not have been set correctly.
>> * If setup_netfront() fails, ensure that all the queues created are
>> cleaned up, not just those that have been set up.
>> * If any queues were set up and an error occurs, call
>> xennet_destroy_queues() to clean up the napi context.
>> * If any fatal error occurs, unregister and destroy the netdev to avoid
>> leaving around a half setup network device.
>>
>> Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
>> ---
>>
>> Changed in V2:
>> * Retested on top of v4.10-rc7 + "xen-netfront: Delete rx_refill_timer
>>   in xennet_disconnect_backend()".
>> * Don't move setup_timer as it is not necessary.
>>
>>  drivers/net/xen-netfront.c | 33 +++++++++++++++------------------
>>  1 file changed, 15 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>> index 722fe9f..5399a86 100644
>> --- a/drivers/net/xen-netfront.c
>> +++ b/drivers/net/xen-netfront.c
>> @@ -1823,27 +1823,23 @@ static int talk_to_netback(struct xenbus_device *dev,
>>  		xennet_destroy_queues(info);
>>
>>  	err = xennet_create_queues(info, &num_queues);
>> -	if (err < 0)
>> -		goto destroy_ring;
>> +	if (err < 0) {
>> +		xenbus_dev_fatal(dev, err, "creating queues");
>> +		if (num_queues > 0) {
>> +			goto destroy_ring;
>
> The only way for us to have (err<0) && (num_queues>0) is when we get a
> -ENOMEM right at the top, isn't it? So there is nothing to disconnect or
> destroy, it seems to me. And if that's true you can directly 'goto out'.
>

You're right, although that might make it a bit more fragile if 
something in xennet_create_queues() changes in the future. Nevertheless, 
I'll update the patch.

-- 
Ross Lagerwall