netdev - Re: [PATCH v8 06/11] net/mlx4_en: add page recycle to prepare rx ring for tx support

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Date:	Wed, 13 Jul 2016 10:17:26 +0300
From:	Tariq Toukan <ttoukan.linux@...il.com>
To:	Brenden Blanco <bblanco@...mgrid.com>,
	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, jhs@...atatu.com,
	saeedm@....mellanox.co.il, kafai@...com, brouer@...hat.com,
	as754m@....com, alexei.starovoitov@...il.com, gerlitz.or@...il.com,
	john.fastabend@...il.com, hannes@...essinduktion.org,
	tgraf@...g.ch, tom@...bertland.com, daniel@...earbox.net
Subject: Re: [PATCH v8 06/11] net/mlx4_en: add page recycle to prepare rx ring
 for tx support


On 13/07/2016 3:54 AM, Brenden Blanco wrote:
> On Tue, Jul 12, 2016 at 02:18:32PM -0700, David Miller wrote:
>> From: Brenden Blanco <bblanco@...mgrid.com>
>> Date: Tue, 12 Jul 2016 00:51:29 -0700
>>
>>> +	mlx4_en_free_resources(priv);
>>> +
>>>   	old_prog = xchg(&priv->prog, prog);
>>>   	if (old_prog)
>>>   		bpf_prog_put(old_prog);
>>>   
>>> -	return 0;
>>> +	err = mlx4_en_alloc_resources(priv);
>>> +	if (err) {
>>> +		en_err(priv, "Failed reallocating port resources\n");
>>> +		goto out;
>>> +	}
>>> +	if (port_up) {
>>> +		err = mlx4_en_start_port(dev);
>>> +		if (err)
>>> +			en_err(priv, "Failed starting port\n");
>> A failed configuration operation should _NEVER_ leave the interface in
>> an inoperative state like these error paths do.
>>
>> You must instead preallocate the necessary resources, and only change
>> the chip's configuration and commit to the new settings once you have
>> successfully allocated those resources.
> I'll see what I can do here.
That's exactly what we're doing in a patchset that will be submitted to 
net very soon (this week).
It fixes/refactors these failure flows just like Dave described, 
something like:

     err = mlx4_en_try_alloc_resources(priv, tmp, &new_prof);
     if (err)
         goto out;

     if (priv->port_up) {
         port_up = 1;
         mlx4_en_stop_port(dev, 1);
     }

     mlx4_en_safe_replace_resources(priv, tmp);

     if (port_up) {
         err = mlx4_en_start_port(dev);
         if (err)
             en_err(priv, "Failed starting port\n");
     }

I suggest you keep your code aligned with current net-next driver, and 
later I will take it and fix it (once merged with net).

Regards,
Tariq