netdev - Re: [PATCH net-next v4 05/24] rocker: use swdev get/set attr for bridge port flags

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Message-ID: <CAE4R7bDoDSeS14Ge1h2mDw-tywdwijkFjqzjF1oe7QGD_8gztw@mail.gmail.com>
Date:	Tue, 14 Apr 2015 23:03:21 -0700
From:	Scott Feldman <sfeldma@...il.com>
To:	Simon Horman <simon.horman@...ronome.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	Jiří Pírko <jiri@...nulli.us>,
	Roopa Prabhu <roopa@...ulusnetworks.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Florian Fainelli <f.fainelli@...il.com>,
	"Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
	"Arad, Ronen" <ronen.arad@...el.com>,
	"andrew@...n.ch" <andrew@...n.ch>
Subject: Re: [PATCH net-next v4 05/24] rocker: use swdev get/set attr for
 bridge port flags

On Tue, Apr 14, 2015 at 10:25 PM, Simon Horman
<simon.horman@...ronome.com> wrote:
> Hi Scott,
>
> On Sun, Apr 12, 2015 at 11:16:59PM -0700, sfeldma@...il.com wrote:
>> From: Scott Feldman <sfeldma@...il.com>
>>
>> Signed-off-by: Scott Feldman <sfeldma@...il.com>
>> ---
>>  drivers/net/ethernet/rocker/rocker.c |   31 +++++++++++++++++++++++++++++--
>>  1 file changed, 29 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/rocker/rocker.c b/drivers/net/ethernet/rocker/rocker.c
>> index 80c7f6f..9bd4fc6 100644
>> --- a/drivers/net/ethernet/rocker/rocker.c
>> +++ b/drivers/net/ethernet/rocker/rocker.c
>
> [snip]
>
>> @@ -4349,6 +4354,23 @@ static void rocker_port_trans_abort(struct rocker_port *rocker_port)
>>       }
>>  }
>>
>> +static int rocker_port_brport_flags_set(struct rocker_port *rocker_port,
>> +                                     unsigned long brport_flags)
>> +{
>> +     unsigned long orig_flags;
>> +     int err = 0;
>> +
>> +     orig_flags = rocker_port->brport_flags;
>> +     rocker_port->brport_flags = brport_flags;
>> +     if ((orig_flags ^ rocker_port->brport_flags) & BR_LEARNING)
>> +             err = rocker_port_set_learning(rocker_port);
>
> My understanding is that the two-phase set scheme that this
> patch-set proposes allows failure, e.g. due resource constraints,
> during the prepare phase but that failure in the commit phase
> indicates a hardware or driver bug.
>
> It seems to me that this patch doesn't follow the above scheme because
> I see the following call-chain:
>
>         rocker_port_set_learning()
>         -> rocker_cmd_exec()
>            -> rocker_wait_create()
>               -> kmalloc()
>
> I am probably missing something but it does seem to me that the above is
> called in both the prepare and commit phases and that kalloc() may fail in
> ether case, the latter case being the problem I see.

Nope, you're not missing something, you found a bug.   A little later
you'll see we use a desc on the cmd ring to issue the cmd to HW.  If
we're in prepare phase, we want to put that desc back on the ring so
commit phase has a desc.  So this needs to be fixed also.  More work
for v5.  But I'm totally glad you're reviewing at this level and
finding issues like this.  Thank you very much.

It's been a little tricky retrofitting rocker for this prepare-commit
scheme.  Prepare phase really forces you to examine all failure paths
and make sure everything is just how you found it and resources are
reserved so commit has a happy life.  My hope is this will be easier
with new drivers knowing the prepare-commit rules up-front.

-scott
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