netdev - Re: [PATCH net-next] switchdev: fix BUG when port driver doesn't support set attr op

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Message-ID: <CAE4R7bBXSMbh4sH+r83H3pDSrhqgvkT4bVfA2t1wEURWUVWzxQ@mail.gmail.com>
Date:	Thu, 11 Jun 2015 08:03:21 -0700
From:	Scott Feldman <sfeldma@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	David Ahern <dsahern@...il.com>, Netdev <netdev@...r.kernel.org>,
	Brenden Blanco <bblanco@...mgrid.com>
Subject: Re: [PATCH net-next] switchdev: fix BUG when port driver doesn't
 support set attr op

On Wed, Jun 10, 2015 at 11:16 PM, Jiri Pirko <jiri@...nulli.us> wrote:
> Thu, Jun 11, 2015 at 12:00:47AM CEST, sfeldma@...il.com wrote:
>>On Wed, Jun 10, 2015 at 2:47 PM, Scott Feldman <sfeldma@...il.com> wrote:
>>> On Wed, Jun 10, 2015 at 2:25 PM, David Ahern <dsahern@...il.com> wrote:
>>>> On 6/10/15 2:56 PM, sfeldma@...il.com wrote:
>>>>>
>>>>> From: Scott Feldman <sfeldma@...il.com>
>>>>>
>>>>> Fix a BUG() where CONFIG_NET_SWITCHDEV is set but the driver for a bridged
>>>>> port does not support switchdec_port_attr_set op.  Don't BUG() if
>>>>> -EOPNOTSUPP is returned.
>>>>>
>>>>> Signed-off-by: Scott Feldman <sfeldma@...il.com>
>>>>> Reported-by: Brenden Blanco <bblanco@...mgrid.com>
>>>>> ---
>>>>>   net/switchdev/switchdev.c |    2 +-
>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/net/switchdev/switchdev.c b/net/switchdev/switchdev.c
>>>>> index e008057..99bced4 100644
>>>>> --- a/net/switchdev/switchdev.c
>>>>> +++ b/net/switchdev/switchdev.c
>>>>> @@ -103,7 +103,7 @@ static void switchdev_port_attr_set_work(struct
>>>>> work_struct *work)
>>>>>
>>>>>         rtnl_lock();
>>>>>         err = switchdev_port_attr_set(asw->dev, &asw->attr);
>>>>> -       BUG_ON(err);
>>>>> +       BUG_ON(err && err != -EOPNOTSUPP);
>>>>>         rtnl_unlock();
>>>>>
>>>>>         dev_put(asw->dev);
>>>>>
>>>>
>>>> Should that be WARN_ON instead of BUG_ON?
>>>
>>> I think I had it as WARN when we were working on the initial patches,
>>> but we changed it to BUG_ON because we should only get an error here
>>> if the driver screwed something up between PREPARE phase and COMMIT
>>> phase, so it should be considered a driver bug which needs fixing.
>>
>>Actually, ignore what I said above.  I was confusing this BUG_ON with
>>the one in switchdev_port_attr_set().  Perhaps this BUG_ON() you're
>>commenting on should be WARN().  A driver could return an err in
>>PREPARE phase and that shouldn't be a BUG_ON situation; seems WARN
>>would be better.   It the case where the driver returns an err in
>>COMMIT phase but didn't return an err in PREPARE phase we want to
>>BUG_ON().  Maybe that case doesn't justify BUG_ON either, based on the
>>link you posted.
>>
>>Jiri, IIRC, you suggested the BUG_ON().  Does it still sound right
>>based on the point David is raising?
>
> Hmm, looking at code of switchdev_port_attr_set. In case that fails in
> prepare state (which can easily happen for example due to -ENOMEM) this
> BUG_ON is hit as well. That is not right. I think we should change it
> just to warning. Also I think that prink (or a flavour) is more suitable
> here than WARN.

Thanks, I'll change it to netdev_err.

> Btw, why switchdev_port_obj_add has WARN and not BUG ?

Not sure.  We should be consistent. WARN seems better for both
obj_add/attr_set than BUG, given the link David Ahern posted.  Do you
agree?
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