On Mon, Oct 12, 2015 at 11:21 PM, Jiri Pirko <j...@resnulli.us> wrote:
> Tue, Oct 13, 2015 at 08:03:46AM CEST, john.fastab...@gmail.com wrote:
>>On 15-10-12 10:44 PM, Jiri Pirko wrote:
>>> Tue, Oct 13, 2015 at 04:52:42AM CEST, sfel...@gmail.com wrote:
>>>> On Mon, Oct 12, 2015 at 11:03 AM, Jiri Pirko <j...@resnulli.us> wrote:
>>>>> From: Jiri Pirko <j...@mellanox.com>
>>>>>
>>>>> Caller should know if he can call attr_set directly (when holding RTNL)
>>>>> or if he has to defer the att_set processing for later.
>>>>>
>>>>> This also allows drivers to sleep inside attr_set and report operation
>>>>> status back to switchdev core. Switchdev core then warns if status is
>>>>> not ok, instead of silent errors happening in drivers.
>>>>>
>>>>> Signed-off-by: Jiri Pirko <j...@mellanox.com>
>>>>> ---
>>>>> include/net/switchdev.h | 1 +
>>>>> net/bridge/br_stp.c | 3 +-
>>>>> net/switchdev/switchdev.c | 107
>>>>> ++++++++++++++++++++++++----------------------
>>>>> 3 files changed, 59 insertions(+), 52 deletions(-)
>>>>>
>>>>> diff --git a/include/net/switchdev.h b/include/net/switchdev.h
>>>>> index d2879f2..6b109e4 100644
>>>>> --- a/include/net/switchdev.h
>>>>> +++ b/include/net/switchdev.h
>>>>> @@ -17,6 +17,7 @@
>>>>>
>>>>> #define SWITCHDEV_F_NO_RECURSE BIT(0)
>>>>> #define SWITCHDEV_F_SKIP_EOPNOTSUPP BIT(1)
>>>>> +#define SWITCHDEV_F_DEFER BIT(2)
>>>>>
>>>>> struct switchdev_trans_item {
>>>>> struct list_head list;
>>>>> diff --git a/net/bridge/br_stp.c b/net/bridge/br_stp.c
>>>>> index db6d243de..80c34d7 100644
>>>>> --- a/net/bridge/br_stp.c
>>>>> +++ b/net/bridge/br_stp.c
>>>>> @@ -41,13 +41,14 @@ void br_set_state(struct net_bridge_port *p, unsigned
>>>>> int state)
>>>>> {
>>>>> struct switchdev_attr attr = {
>>>>> .id = SWITCHDEV_ATTR_ID_PORT_STP_STATE,
>>>>> + .flags = SWITCHDEV_F_DEFER,
>>>>> .u.stp_state = state,
>>>>> };
>>>>> int err;
>>>>>
>>>>> p->state = state;
>>>>> err = switchdev_port_attr_set(p->dev, &attr);
>>>>> - if (err && err != -EOPNOTSUPP)
>>>>> + if (err)
>>>>
>>>> This looks like a problem as now all other non-switchdev ports will
>>>> get an WARN in the log when STP state changes. We should only WARN if
>>>> there was an err and the err is not -EOPNOTSUPP.
>>>
>>> If SWITCHDEV_F_DEFER flag is set, there's only 0 of -ENOMEM.
>>>
>>>
>>>>
>>>>> br_warn(p->br, "error setting offload STP state on port
>>>>> %u(%s)\n",
>>>>> (unsigned int) p->port_no, p->dev->name);
>>>>> }
>>>>
>>>> <snip>
>>>>
>>>>> struct switchdev_attr_set_work {
>>>>> struct work_struct work;
>>>>> struct net_device *dev;
>>>>> @@ -183,14 +226,17 @@ static void switchdev_port_attr_set_work(struct
>>>>> work_struct *work)
>>>>> {
>>>>> struct switchdev_attr_set_work *asw =
>>>>> container_of(work, struct switchdev_attr_set_work, work);
>>>>> + bool rtnl_locked = rtnl_is_locked();
>>>>> int err;
>>>>>
>>>>> - rtnl_lock();
>>>>> - err = switchdev_port_attr_set(asw->dev, &asw->attr);
>>>>> + if (!rtnl_locked)
>>>>> + rtnl_lock();
>>>>
>>>> I'm not following this change. If someone else has rtnl_lock, we'll
>>>> not wait to grab it here ourselves, and proceed as if we have the
>>>> lock. But what if that someone else releases the lock in the middle
>>>> of us doing switchdev_port_attr_set_now? Seems we want to
>>>> unconditionally wait and grab the lock. We need to block anything
>>>>from moving while we do the attr set.
>>>
>>> Why would someone we call (driver) return the lock? In that case, he is
>>> buggy and should be fixed.
>>>
>>> This hunk only ensures we have rtnl_lock. If not, we take it here. We do
>>> not take it unconditionally because we may already have it, for example
>>> if caller of switchdev_flush_deferred holds rtnl_lock.
>>>
>>
>>This is where you lost me. How do you know another core doesn't happen
>>to have the lock when you hit this code path? Maybe someone is running
>>an ethtool command on another core or something.
>
> You are right. The same problem exists currently in switchdev_port_attr_set.
You are right as in you'll change this back to unconditional grabbing
of rtnl_lock? I don't follow how this problem currently exists as
current code does an unconditional grab of rtnl_lock.
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