On 15-10-12 10:45 PM, Jiri Pirko wrote:
> Tue, Oct 13, 2015 at 06:40:25AM CEST, john.fastab...@gmail.com wrote:
>> On 15-10-12 07:52 PM, Scott Feldman 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.
>>>
>>>> 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.
>>>
>>
>> Also an additional race between setting rtnl_locked and the if stmt
>> and then grabbing the lock. There seems to be a something of pattern
>> around this where other subsystems use a rtnl_trylock and if it fails
>> do a restart/re-queue operation to retry. Looks like how you handle
>> it in the team driver at least.
>
> No, this is for different case. This is for case someone calls
> switchdev_flush_defererd holding the rtnl_lock.
>
OK rather than funky if stmt could you just do a rtnl_trylock() and
put a comment explaining the reasoning?
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